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Full vulnerability report · 2026
CVE-2026-42791High confidence

OCSP responder certificate validity period not checked in public_key

Erlang · OTP

Official source article: GitHub GHSA-CJXJ-WJ6X-3FFF ↗. Check the applicable product and release in the original source.

6.3MediumCVSS 4.0
Recommended action
Scheduled

Medium technical severity with no CISA KEV confirmation; remediate through the normal risk-based patch cycle unless local exposure raises the priority.

Patch available
R
Operational reassessment

Published severity in operational context

Open reassessment dashboard →
Published severityMediumOperational priority:Medium, unchanged from published severity.unchanged

Evidence used

  • No CISA KEV confirmation is currently recorded.
  • The selected CVSS metric records a network-reachable, unauthenticated path with no user interaction.
  • EPSS is 0.32% for the current model date.

Compensating controls

  • Validate the affected product branch and deploy the verified fixed release.
  • Restrict the affected network interface to trusted sources where business-safe.
  • Monitor vendor guidance and exploitation sources for a material change.

Verification

  1. Confirm that the asset runs Erlang OTP and falls inside the recorded affected range.
  2. Verify the installed build against the product-specific fixed version after deployment.
  3. Validate exposure, authentication requirements and compensating controls in the actual environment.
  4. Reopen this reassessment when CVSS, KEV, EPSS, exploit evidence or remediation changes.
Mitigation target: As exposure requiresRemediation target: Within 365 days

This automated reassessment organises public evidence. It does not know asset exposure, business impact or control effectiveness and does not replace CVSS or a human risk decision.

Distribution package intelligence

Release-specific package status

Debian, ubuntu findings are scoped to the named distribution, release and source package. An absent finding does not mean a package is unaffected.

5 package states
Repository candidate not checked

A published vendor fix does not prove that a matching update is enabled and installable on a particular asset. Confirm the local package candidate before scheduling remediation.

Distribution releaseSource packageVendor stateFixed versionEvidence
Debian trixietrixie · sourceerlangVendor fix publishedDebian records a fixed source-package version for this release.1:27.3.4.1+dfsg-1+deb13u3Debian Security Tracker ↗Source updated 5 Oct 2026
Debian bookwormbookworm · sourceerlangNot affectedDebian marks this release not affected (fixed-version marker 0).Not published in this feedDebian Security Tracker ↗Source updated 5 Oct 2026
Debian forkyforky · sourceerlangVendor fix publishedDebian records a fixed source-package version for this release.1:27.3.4.12+dfsg-1Debian Security Tracker ↗Source updated 5 Oct 2026
Debian sidsid · sourceerlangVendor fix publishedDebian records a fixed source-package version for this release.1:27.3.4.12+dfsg-1Debian Security Tracker ↗Source updated 5 Oct 2026
Ubuntu 24.04 LTSnoble · standard archiveerlangUnder evaluationCanonical reports that the package might be affected and still needs evaluation or fixing.Not published in this feedCanonical Ubuntu Security ↗Source updated 5 Oct 2026
Direct vendor intelligence

Authoritative vendor CSAF and VEX advisories

Structured product status and remediation from the issuing vendor. Product-state explanations are always visible; large lists can be searched or downloaded.

1 current
CVE-2026-42791 · CSAF 2.0 · revision 3 · finalRed Hat Product Securityerlang: Erlang OTP: Authentication bypass due to improper OCSP certificate validation
79 fixed

The vendor explicitly identifies these products or versions as containing the fix.

  • erlang27-0:27.3.4.17-1.hum1@aarch64 as a component of Red Hat Hardened Images
  • erlang27-0:27.3.4.17-1.hum1@src as a component of Red Hat Hardened Images
  • erlang27-0:27.3.4.17-1.hum1@x86_64 as a component of Red Hat Hardened Images
  • erlang27-asn1-0:27.3.4.17-1.hum1@aarch64 as a component of Red Hat Hardened Images
  • erlang27-asn1-0:27.3.4.17-1.hum1@x86_64 as a component of Red Hat Hardened Images
  • erlang27-common_test-0:27.3.4.17-1.hum1@aarch64 as a component of Red Hat Hardened Images
  • erlang27-common_test-0:27.3.4.17-1.hum1@x86_64 as a component of Red Hat Hardened Images
  • erlang27-compiler-0:27.3.4.17-1.hum1@aarch64 as a component of Red Hat Hardened Images
  • erlang27-compiler-0:27.3.4.17-1.hum1@x86_64 as a component of Red Hat Hardened Images
  • erlang27-crypto-0:27.3.4.17-1.hum1@aarch64 as a component of Red Hat Hardened Images
  • erlang27-crypto-0:27.3.4.17-1.hum1@x86_64 as a component of Red Hat Hardened Images
  • erlang27-debugger-0:27.3.4.17-1.hum1@aarch64 as a component of Red Hat Hardened Images
Summary
A flaw was found in Erlang OTP's public_key application, specifically in the Online Certificate Status Protocol (OCSP) response verification. A remote attacker who has obtained the private key of an expired Certificate Authority (CA)-designated OCSP responder certificate can forge OCSP responses. This allows a malicious server to present a revoked Transport Layer Security (TLS) certificate, which a client would then accept as valid, leading to an authentication bypass. This vulnerability can also affect applications directly using the public_key:pkix_ocsp_validate/5 API, potentially enabling authentication bypass with revoked client certificates.
Remediation
For details on how to apply this update, which includes the changes described in this advisory, refer to: https://images.redhat.com/
Optional official sources

National CERT insights
?CERT means Computer Emergency Response Team; CSIRT is the closely related term Computer Security Incident Response Team.

Choose official national sources for this report. Each advisory shows its original language. Your selection is remembered on this device and included in shared links.

Official European source

ENISA European Vulnerability Database

Official EUVD identifiers, advisory evidence and known-exploited context. Missing fields are not treated as evidence of low risk.

1 current
ENISA EUVD identifier

EUVD-2026-32273

No EUVD known-exploited evidence

ENISA has published the identifier mapping but no EUVD description has been stored yet.

EUVD state
Present in the current official mapping
Known exploitation
Not present in the current ENISA EUVD known-exploited dataset. This is not proof of no exploitation.
ENISA score
Not supplied in the stored EUVD record
Advisory evidence
No linked advisory details stored yet
Recommended actionScheduled

Medium technical severity with no CISA KEV confirmation; remediate through the normal risk-based patch cycle unless local exposure raises the priority.

Patch available
01

What, why and how

Improper Certificate Validation vulnerability in Erlang OTP public_key (pubkey_ocsp module) allows forged OCSP responses signed with an expired responder certificate to be accepted as valid. OCSP response verification in pubkey_ocsp:verify_response/5 and pubkey_ocsp:is_authorized_responder/3 in lib/public_key/src/pubkey_ocsp.erl does not check the validity period (notBefore/notAfter) of the OCSP responder certificate. An attacker who has obtained the private key of an expired CA-designated OCSP responder certificate can forge OCSP responses that Erlang/OTP accepts as valid. This affects TLS clients using OCSP stapling via the ssl application: a malicious or compromised server can present a revoked TLS certificate together with a forged OCSP response signed by an expired responder key, and the client will accept the revoked certificate as valid. It also affects applications calling public_key:pkix_ocsp_validate/5 directly, where the impact depends on the use case — server-side client certificate validation using this API may allow authentication bypass with a revoked client certificate. This issue affects OTP from OTP 27.0 before OTP 29.0.1, OTP 28.5.0.1 and OTP 27.3.4.12, corresponding to public_key from 1.16 before 1.21.1, 1.20.3.1 and 1.17.1.3.

What

Improper Certificate Validation vulnerability in Erlang OTP public_key (pubkey_ocsp module) allows forged OCSP responses signed with an expired responder certificate to be accepted as valid. OCSP response verification in pubkey_ocsp:verify_response/5 and pubkey_ocsp:is_authorized_responder/3 in lib/public_key/src/pubkey_ocsp.erl does not check the validity period (notBefore/notAfter) of the OCSP responder certificate. An attacker who has obtained the private key of an expired CA-designated OCSP responder certificate can forge OCSP responses that Erlang/OTP accepts as valid. This affects TLS clients using OCSP stapling via the ssl application: a malicious or compromised server can present a revoked TLS certificate together with a forged OCSP response signed by an expired responder key, and the client will accept the revoked certificate as valid. It also affects applications calling public_key:pkix_ocsp_validate/5 directly, where the impact depends on the use case — server-side client certificate validation using this API may allow authentication bypass with a revoked client certificate. This issue affects OTP from OTP 27.0 before OTP 29.0.1, OTP 28.5.0.1 and OTP 27.3.4.12, corresponding to public_key from 1.16 before 1.21.1, 1.20.3.1 and 1.17.1.3.

Why

The product does not validate, or incorrectly validates, a certificate.

How

An attacker operating through a network path may attempt exploitation without authentication or user interaction. If successful, the issue may bypass an access boundary or take over an account.

What

Improper Certificate Validation vulnerability in Erlang OTP public_key (pubkey_ocsp module) allows forged OCSP responses signed with an expired responder certificate to be accepted as valid. OCSP response verification in pubkey_ocsp:verify_response/5 and pubkey_ocsp:is_authorized_responder/3 in lib/public_key/src/pubkey_ocsp.erl does not check the validity period (notBefore/notAfter) of the OCSP responder certificate. An attacker who has obtained the private key of an expired CA-designated OCSP responder certificate can forge OCSP responses that Erlang/OTP accepts as valid. This affects TLS clients using OCSP stapling via the ssl application: a malicious or compromised server can present a revoked TLS certificate together with a forged OCSP response signed by an expired responder key, and the client will accept the revoked certificate as valid. It also affects applications calling public_key:pkix_ocsp_validate/5 directly, where the impact depends on the use case — server-side client certificate validation using this API may allow authentication bypass with a revoked client certificate. This issue affects OTP from OTP 27.0 before OTP 29.0.1, OTP 28.5.0.1 and OTP 27.3.4.12, corresponding to public_key from 1.16 before 1.21.1, 1.20.3.1 and 1.17.1.3.

Why

The product does not validate, or incorrectly validates, a certificate.

How

An attacker operating through a network path may attempt exploitation without authentication or user interaction. If successful, the issue may bypass an access boundary or take over an account.

02

Exploit reality and attack path

CVSS severity, EPSS forecast probability, public exploit material and CISA-confirmed exploitation are separate signals.

Observed exploitation
?Confirmed exploitation and public exploit material are separate signals. Attacks can occur without public proof-of-concept or exploit code.
No confirmed evidence

No CISA KEV match was present at the last successful refresh. This means no confirmation from that source, not proof of no exploitation.

Public PoC / exploit material
?Confirmed exploitation and public exploit material are separate signals. Attacks can occur without public proof-of-concept or exploit code.
None recorded

No exploit-tagged reference or CISA SSVC proof-of-concept state is currently recorded. Research may still exist outside the structured feeds.

Likely attack path
a network path → Improper Certificate Validation → bypass an access boundary or take over an account
Attack surface
Network
Privileges required
None: unauthenticated exploitation is possible
User interaction
None
Attack complexity
High: exploitation depends on specific conditions
Security boundary
Not a CVSS 4.0 base metric
Weakness
?CWE means Common Weakness Enumeration: a standard category for the underlying weakness.
CWE-295 ↗

CWE-295: Improper Certificate Validation. The product does not validate, or incorrectly validates, a certificate.

CVSS vector
?CVSS means Common Vulnerability Scoring System. The vector records the metric values used to calculate technical severity.
CVSS:4.0/AV:N/AC:H/AT:P/PR:N/UI:N/VC:N/VI:L/VA:N/SC:L/SI:L/SA:N

Common Vulnerability Scoring System 4.0: the compact vector below is decoded into plain language.

AVNetworkAttack vector: The vulnerable component can be reached over a network.ACHighAttack complexity: Successful exploitation depends on specific conditions outside the attacker's direct control.ATPresentAttack requirements: A particular deployment or execution condition must be present.PRNonePrivileges required: The attacker does not need an account or existing privileges.UINoneUser interaction: No action by another user is required.VCNoneVulnerable-system confidentiality: No direct loss is represented by this metric.VILowVulnerable-system integrity: A successful attack can cause a limited loss.VANoneVulnerable-system availability: No direct loss is represented by this metric.SCLowSubsequent-system confidentiality: A successful attack can cause a limited loss.SILowSubsequent-system integrity: A successful attack can cause a limited loss.SANoneSubsequent-system availability: No direct loss is represented by this metric.
Post-exploitation / living off the land
Stolen credentials, tokens and legitimate administration functions may provide continued access without deploying a large custom toolset.
NetworkUnauthenticatedCWE-295
A

Official authority intelligence

Only matched European and national findings are included. Language selectors and unavailable sources are omitted.

BSI · German · WID-SEC-2026-1719Erlang/OTP: Mehrere Schwachstellen ermöglichen Umgehen von Sicherheitsvorkehrungen

Ein entfernter, anonymer Angreifer kann mehrere Schwachstellen in Erlang/OTP ausnutzen, um Sicherheitsvorkehrungen zu umgehen.

Official advisory ↗
Cyber Security Agency of Singapore · English · CSA-SB-20260603Security Bulletin 3 Jun 2026

The Cyber Security Agency of Singapore included this CVE in its official Security Bulletin 3 Jun 2026, published on 3 June 2026. Open the linked bulletin for the product, severity and reference information published in that issue.

Official advisory ↗
JVN iPedia · Japanese · JVNDB-2026-017840ERLANGのErlang/OTPにおける複数の脆弱性

Erlang OTPのpublic_keyモジュール(pubkey_ocspモジュール)における不適切な証明書検証の脆弱性により、有効期限切れのレスポンダー証明書で署名された偽造OCSPレスポンスが有効として受け入れられる可能性があります。lib/public_key/src/pubkey_ocsp.erl内のpubkey_ocsp:verify_response/5およびpubkey_ocsp:is_authorized_responder/3によるOCSPレスポンスの検証は、OCSPレスポンダー証明書の有効期間(notBefore/notAfter)をチェックしていません。有効期限切れのCA指定OCSPレスポンダー証明書の秘密鍵を取得した攻撃者は、Erlang/OTPが有効と受け入れる偽造OCSPレスポンスを作成可能です。これは、sslアプリケーション経由でOCSPステープリングを使用するTLSクライアントに影響します。悪意のあるまたは侵害されたサーバーは、失効したTLS証明書を偽造されたOCSPレスポンス（有効期限切れのレスポンダー鍵で署名されたもの）と共に提示でき、クライアントはその失効証明書を有効として受け入れます。また、public_key:pkix_ocsp_validate/5を直接呼び出すアプリケーションにも影響があり、その影響はユースケースによって異なります。サーバー側のクライアント証明書検証でこのAPIを使用している場合、失効したクライアント証明書による認証回避を許す可能性があります。この問題は、OTP 27.0から27.3.4.12、28.5.0.1、29.0.1のpublic_key 1.16以前から1.17.1.3、1.20.3.1、1.21.1に対応するOTPのバージョンに影響します。

Official advisory ↗
03

Patch and workaround

Operational remediation based on structured source evidence.

Status
?Patch availability is based on structured fixed-version fields and authoritative update references. If no fix is verified, check the vendor advisory before making a change.
Patch available
Affected
OTP: 1.16 < *, 27.0 < *, 2b1a742c651b90f8a7a1fb2ddde73f29915ea376 < *
Fixed
Action
For details on how to apply this update, which includes the changes described in this advisory, refer to: https://images.redhat.com/
Workaround
No verified workaround is recorded. If business-safe, reduce exposure to the affected interface and allow only trusted sources until authoritative guidance is available.
04

Evidence and provenance

Published 27 May 2026 · Last source change 24 Jul 2026, 14:14 UTC · CWE-295 · Improper Certificate Validation

CVE recordCVE.org · 5.2
CVSS sourceCNA
EPSS source
?The date BlackTree first stored a score for this CVE from the daily FIRST EPSS feed.
FIRST · tracked since 2026-08-14
European sourceENISA EUVD · EUVD-2026-32273
Product sourceCNA
Remediation sourceVendor CSAF · Red Hat Product Security
CWE sourceCNA
NVD statusNVD modified after enrichment

Core structured fields are present and their contributing authorities are shown above.

Material change intelligence

What changed after publication

View recent updates ↗
  1. Affected versionsThe structured affected or fixed version information changed.
    Before
    1.16 < *; 27.0 < *; 2b1a742c651b90f8a7a1fb2ddde73f29915ea376 < * · Fixed: An authoritative update reference is available, but the fixed version is not recorded in the structured CVE fields. Check the linked vendor advisory for the applicable release.
    After
    1.16 < *; 27.0 < *; 2b1a742c651b90f8a7a1fb2ddde73f29915ea376 < * · Fixed: For details on how to apply this update, which includes the changes described in this advisory, refer to: https://images.redhat.com/
    Red Hat Product Security ↗
  2. Vendor guidanceAuthoritative vendor guidance changed from remediation: access.redhat.com/CVE-2026-42791 to remediation: access.redhat.com/CVE-2026-42791.
    Before
    remediation: access.redhat.com/CVE-2026-42791
    After
    remediation: access.redhat.com/CVE-2026-42791
    Red Hat Product Security ↗
  3. Remediation statusRemediation status changed from Mitigation available to Patch available.
    Before
    Mitigation available
    After
    Patch available
    Red Hat Product Security ↗
  4. Affected versionsThe structured affected or fixed version information changed.
    Before
    erlang27.src as a component of Red Hat Hardened Images
    After
    Fixed: erlang27-0:27.3.4.17-1.hum1@aarch64 as a component of Red Hat Hardened Images; erlang27-0:27.3.4.17-1.hum1@src as a component of Red Hat Hardened Images; erlang27-0:27.3.4.17-1.hum1@x86_64 as a component of Red Hat Hardened Images; erlang27-asn1-0:27.3.4.17-1.hum1@aarch64 as a component of Red Hat Hardened Images; erlang27-asn1-0:27.3.4.17-1.hum1@x86_64 as a component of Red Hat Hardened Images; erlang27-common_test-0:27.3.4.17-1.hum1@aarch64 as a component of Red Hat Hardened Images; erlang27-common_test-0:27.3.4.17-1.hum1@x86_64 as a component of Red Hat Hardened Images; erlang27-compiler-0:27.3.4.17-1.hum1@aarch64 as a component of Red Hat Hardened Images; erlang27-compiler-0:27.3.4.17-1.hum1@x86_64 as a component of Red Hat Hardened Images; erlang27-crypto-0:27.3.4.17-1.hum1@aarch64 as a component of Red Hat Hardened Images; erlang27-crypto-0:27.3.4.17-1.hum1@x86_64 as a component of Red Hat Hardened Images; erlang27-debugger-0:27.3.4.17-1.hum1@aarch64 as a component of Red Hat Hardened Images; erlang27-debugger-0:27.3.4.17-1.hum1@x86_64 as a component of Red Hat Hardened Images; erlang27-dialyzer-0:27.3.4.17-1.hum1@aarch64 as a component of Red Hat Hardened Images; erlang27-dialyzer-0:27.3.4.17-1.hum1@x86_64 as a component of Red Hat Hardened Images; erlang27-diameter-0:27.3.4.17-1.hum1@aarch64 as a component of Red Hat Hardened Images; erlang27-diameter-0:27.3.4.17-1.hum1@x86_64 as a component of Red Hat Hardened Images; erlang27-edoc-0:27.3.4.17-1.hum1@aarch64 as a component of Red Hat Hardened Images; erlang27-edoc-0:27.3.4.17-1.hum1@x86_64 as a component of Red Hat Hardened Images; erlang27-eldap-0:27.3.4.17-1.hum1@aarch64 as a component of Red Hat Hardened Images; erlang27-eldap-0:27.3.4.17-1.hum1@x86_64 as a component of Red Hat Hardened Images; erlang27-erl_interface-0:27.3.4.17-1.hum1@aarch64 as a component of Red Hat Hardened Images; erlang27-erl_interface-0:27.3.4.17-1.hum1@x86_64 as a component of Red Hat Hardened Images; erlang27-erts-0:27.3.4.17-1.hum1@aarch64 as a component of Red Hat Hardened Images; erlang27-erts-0:27.3.4.17-1.hum1@x86_64 as a component of Red Hat Hardened Images; erlang27-et-0:27.3.4.17-1.hum1@aarch64 as a component of Red Hat Hardened Images; erlang27-et-0:27.3.4.17-1.hum1@x86_64 as a component of Red Hat Hardened Images; erlang27-eunit-0:27.3.4.17-1.hum1@aarch64 as a component of Red Hat Hardened Images; erlang27-eunit-0:27.3.4.17-1.hum1@x86_64 as a component of Red Hat Hardened Images; erlang27-examples-0:27.3.4.17-1.hum1@aarch64 as a component of Red Hat Hardened Images; and 49 more
    Red Hat Product Security ↗
Material fields only · duplicate refreshes suppressed · history retained for the configured operational retention period
CVE published
Fixed release or patch reference recorded
Fixed release recorded from official guidance
ENISA EUVD · EUVD-2026-32273↗Red Hat Product Security security advisory↗CVE authority or vendor reference · GitHub GHSA-CJXJ-WJ6X-3FFF↗Patch or update reference↗Patch or update reference↗Official CVE record (CNA and ADP data)↗NVD record↗
Technical terms and abbreviations used in this report
CVE
Common Vulnerabilities and Exposures: the public identifier for one disclosed vulnerability.
CVSS
Common Vulnerability Scoring System: a technical severity framework; it is not patching priority by itself.
EPSS
Exploit Prediction Scoring System: FIRST's estimate of the probability that exploitation activity will be observed in the next 30 days; it is a forecast, not confirmation.
CWE
Common Weakness Enumeration: the standard category describing the underlying software or hardware weakness.
CNA
CVE Numbering Authority: an organisation authorised to assign and publish CVE records.
CISA ADP
Cybersecurity and Infrastructure Security Agency Authorized Data Publisher: structured enrichment added to a CVE record.
NVD
National Vulnerability Database: NIST's enrichment service for CVE records.
CERT / CSIRT
A computer security incident response team that publishes warnings or coordinates incident response.
PoC
Proof of concept: public material that demonstrates or helps reproduce exploitation.
CSAF
Common Security Advisory Framework: a machine-readable format for security advisories.
LoTL
Living off the land: abuse of legitimate tools or system functions during an attack.
Free version - for non-commercial use only.CVE-2026-42791 · cve.blacktree.nl