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Full vulnerability report · 2026
CVE-2026-39984High confidence

Sigstore Timestamp Authority has Improper Certificate Validation in verifier

sigstore · timestamp-authority

Official source article: GitHub GHSA-XM5M-WGH2-RRG3 ↗. Check the applicable product and release in the original source.

5.5MediumCVSS 3.1
Recommended action
Patch only the product branches with a verified fix

Medium technical severity with no CISA KEV confirmation; remediate through the normal risk-based patch cycle unless local exposure raises the priority. Verified remediation exists for at least one product or source, but 10 structured product or package states remain unresolved. Apply remediation only to the exact product branch confirmed by its source.

Fix availability varies by product
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.
  • EPSS is 0.11% for the current model date.

Compensating controls

  • Validate the affected product branch and deploy the verified fixed release.
  • Restrict local access and enforce least privilege on affected hosts.
  • Monitor vendor guidance and exploitation sources for a material change.

Verification

  1. Confirm that the asset runs sigstore timestamp-authority 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.

Cross-source reconciliation

Remediation availability differs by product scope

Verified remediation exists for at least one product or source, but 10 structured product or package states remain unresolved. Apply remediation only to the exact product branch confirmed by its source.

Distribution package intelligence

Release-specific package status

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

3 package states
Package result overrides the generic status

BlackTree has verified remediation for at least one product or source, but the relevant distribution still reports no fixed package for 1 affected package state shown here. Treat those rows as affected with no fix until that distribution publishes a fixed version.

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 · sourcegolang-github-sigstore-timestamp-authorityAffected, no fix publishedDebian currently tracks this release as open.Not published in this feedDebian Security Tracker ↗Source updated 6 Oct 2026
Debian forkyforky · sourcegolang-github-sigstore-timestamp-authorityVendor fix publishedDebian records a fixed source-package version for this release.2.1.0-1Debian Security Tracker ↗Source updated 6 Oct 2026
Debian sidsid · sourcegolang-github-sigstore-timestamp-authorityVendor fix publishedDebian records a fixed source-package version for this release.2.1.0-1Debian Security Tracker ↗Source updated 6 Oct 2026
Open-source package ranges2 source-attributed ranges

These OSV and GitHub advisory ranges apply only to the named package and ecosystem. A listed fixed version is not a universal product patch or proof that an update is installed.

Ecosystem and packageAffected rangeFirst fixed versionEvidence
Gogithub.com/sigstore/timestamp-authority/v2SEMVER: introduced 0; fixed 2.0.62.0.6OSV record ↗aggregator derived · 10 Sep 2026
gogithub.com/sigstore/timestamp-authority/v2<= 2.0.52.0.6GitHub advisory ↗upstream repository advisory · 24 Apr 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.

2 current
CVE-2026-39984 · CSAF 2.0 · revision 13 · interimSUSE Product Security TeamCVE-2026-39984
46 known affected

The vendor explicitly identifies these products as affected by this CVE.

  • cosign as component of SUSE Linux Enterprise Desktop 15 SP7
  • cosign-bash-completion as component of SUSE Linux Enterprise Desktop 15 SP7
  • cosign-zsh-completion as component of SUSE Linux Enterprise Desktop 15 SP7
  • cosign as component of SUSE Linux Enterprise High Performance Computing 15 SP4-LTSS
  • cosign as component of SUSE Linux Enterprise High Performance Computing 15 SP4
  • cosign as component of SUSE Linux Enterprise High Performance Computing 15 SP5-LTSS
  • cosign as component of SUSE Linux Enterprise High Performance Computing 15 SP5
  • cosign as component of SUSE Linux Enterprise Module for Basesystem 15 SP7
  • cosign-bash-completion as component of SUSE Linux Enterprise Module for Basesystem 15 SP7
  • cosign-zsh-completion as component of SUSE Linux Enterprise Module for Basesystem 15 SP7
  • cosign as component of SUSE Linux Enterprise Server 15 SP4-LTSS
  • cosign as component of SUSE Linux Enterprise Server 15 SP4
Summary
Sigstore Timestamp Authority is a service for issuing RFC 3161 timestamps. Versions 2.0.5 and below contain an authorization bypass vulnerability in the VerifyTimestampResponse function. VerifyTimestampResponse correctly verifies the certificate chain signature, but the TSA-specific constraint checks in VerifyLeafCert uses the first non-CA certificate from the PKCS#7 certificate bag instead of the leaf certificate from the verified chain. An attacker can exploit this by prepending a forged certificate to the certificate bag while the message is signed with an authorized key, causing the library to validate the signature against one certificate but perform authorization checks against another. This vulnerability only affects users of the timestamp-authority/v2/pkg/verification package and does not affect the timestamp-authority service itself or sigstore-go. The issue has been fixed in version 2.0.6.
Remediation
To install this SUSE Security Update use the SUSE recommended installation methods like YaST online_update or "zypper patch".
CVE-2026-39984 · CSAF 2.0 · revision 3 · finalRed Hat Product Securitytimestamp-authority/v2/pkg/verification: improper certificate validation in verifier
9 known affected

The vendor explicitly identifies these products as affected by this CVE.

  • advanced-cluster-security/rhacs-main-rhel8 as a component of Red Hat Advanced Cluster Security 4
  • advanced-cluster-security/rhacs-rhel8-operator as a component of Red Hat Advanced Cluster Security 4
  • advanced-cluster-security/rhacs-roxctl-rhel8 as a component of Red Hat Advanced Cluster Security 4
  • advanced-cluster-security/rhacs-scanner-v4-rhel8 as a component of Red Hat Advanced Cluster Security 4
  • rhtas/cosign-rhel9 as a component of Red Hat Trusted Artifact Signer
  • rhtas/ec-rhel9 as a component of Red Hat Trusted Artifact Signer
  • rhtas/gitsign-rhel9 as a component of Red Hat Trusted Artifact Signer
  • compliance/openshift-security-profiles-operator-bundle as a component of Security Profiles Operator
  • compliance/openshift-security-profiles-rhel8-operator as a component of Security Profiles Operator
Summary
A flaw was found in timestamp-authority, specifically in the timestamp-authority/v2/pkg/verification package. An attacker can exploit this issue by prepending a forged certificate to the certificate bag while the message is signed with an authorized key. This causes the library to validate the signature against one certificate but perform authorization checks against another, leading to an authorization bypass.
Remediation
To mitigate this vulnerability, users of VerifyTimestampResponse can use the TSACertificate option to explicitly specify the exact certificate they expect to be used.
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-2026-22813

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 actionPatch only the product branches with a verified fix

Medium technical severity with no CISA KEV confirmation; remediate through the normal risk-based patch cycle unless local exposure raises the priority. Verified remediation exists for at least one product or source, but 10 structured product or package states remain unresolved. Apply remediation only to the exact product branch confirmed by its source.

Fix availability varies by product
01

What, why and how

Sigstore Timestamp Authority is a service for issuing RFC 3161 timestamps. Versions 2.0.5 and below contain an authorization bypass vulnerability in the VerifyTimestampResponse function. VerifyTimestampResponse correctly verifies the certificate chain signature, but the TSA-specific constraint checks in VerifyLeafCert uses the first non-CA certificate from the PKCS#7 certificate bag instead of the leaf certificate from the verified chain. An attacker can exploit this by prepending a forged certificate to the certificate bag while the message is signed with an authorized key, causing the library to validate the signature against one certificate but perform authorization checks against another. This vulnerability only affects users of the timestamp-authority/v2/pkg/verification package and does not affect the timestamp-authority service itself or sigstore-go. The issue has been fixed in version 2.0.6.

What

Sigstore Timestamp Authority is a service for issuing RFC 3161 timestamps. Versions 2.0.5 and below contain an authorization bypass vulnerability in the VerifyTimestampResponse function. VerifyTimestampResponse correctly verifies the certificate chain signature, but the TSA-specific constraint checks in VerifyLeafCert uses the first non-CA certificate from the PKCS#7 certificate bag instead of the leaf certificate from the verified chain. An attacker can exploit this by prepending a forged certificate to the certificate bag while the message is signed with an authorized key, causing the library to validate the signature against one certificate but perform authorization checks against another. This vulnerability only affects users of the timestamp-authority/v2/pkg/verification package and does not affect the timestamp-authority service itself or sigstore-go. The issue has been fixed in version 2.0.6.

Why

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

How

An attacker operating through local access may attempt exploitation without authentication after a user interaction. If successful, the issue may cause the confidentiality, integrity or availability impact described by the vendor.

What

Sigstore Timestamp Authority is a service for issuing RFC 3161 timestamps. Versions 2.0.5 and below contain an authorization bypass vulnerability in the VerifyTimestampResponse function. VerifyTimestampResponse correctly verifies the certificate chain signature, but the TSA-specific constraint checks in VerifyLeafCert uses the first non-CA certificate from the PKCS#7 certificate bag instead of the leaf certificate from the verified chain. An attacker can exploit this by prepending a forged certificate to the certificate bag while the message is signed with an authorized key, causing the library to validate the signature against one certificate but perform authorization checks against another. This vulnerability only affects users of the timestamp-authority/v2/pkg/verification package and does not affect the timestamp-authority service itself or sigstore-go. The issue has been fixed in version 2.0.6.

Why

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

How

An attacker operating through local access may attempt exploitation without authentication after a user interaction. If successful, the issue may cause the confidentiality, integrity or availability impact described by the vendor.

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
local access → Improper Certificate Validation → cause the confidentiality, integrity or availability impact described by the vendor
Attack surface
Local
Privileges required
None: unauthenticated exploitation is possible
User interaction
Required interaction required
Attack complexity
Low: no specialised conditions are recorded
Security boundary
Unchanged: impact remains within the vulnerable component's security authority
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:3.1/AV:L/AC:L/PR:N/UI:R/S:U/C:N/I:H/A:N

Common Vulnerability Scoring System 3.1: the compact vector below is decoded into plain language.

AVLocalAttack vector: The attacker needs local access to the vulnerable system.ACLowAttack complexity: No specialised conditions are required beyond attacker-controlled input.PRNonePrivileges required: The attacker does not need an account or existing privileges.UIRequiredUser interaction: Another user must perform an action for exploitation to succeed.SUnchangedScope: The security impact remains within the vulnerable component's authority.CNoneConfidentiality impact: No direct loss is represented by this metric.IHighIntegrity impact: A successful attack can cause a major loss.ANoneAvailability impact: No direct loss is represented by this metric.
Post-exploitation / living off the land
The issue can support a local privilege or sandbox boundary transition; normal system utilities may then be available in the gained context.
UnauthenticatedCWE-295
A

Official authority intelligence

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

BSI · German · WID-SEC-2026-3046IBM Concert: Mehrere Schwachstellen

Ein Angreifer kann mehrere Schwachstellen in IBM Concert ausnutzen, um beliebigen Programmcode auszuführen, um einen Denial of Service Angriff durchzuführen, um Informationen offenzulegen, um Dateien zu manipulieren, um einen Cross-Site Scripting Angriff durchzuführen, um einen SQL-Injection Angriff durchzuführen und um Sicherheitsvorkehrungen zu umgehen.

Official advisory ↗
Cyber Security Agency of Singapore · English · CSA-SB-20260422Security Bulletin 22 April 2026

The Cyber Security Agency of Singapore included this CVE in its official Security Bulletin 22 April 2026, published on 22 April 2026. Open the linked bulletin for the product, severity and reference information published in that issue.

Official advisory ↗
JVN iPedia · Japanese · JVNDB-2026-012825Linux FoundationのSigstore Timestamp Authorityにおける証明書検証に関する脆弱性

Sigstore Timestamp AuthorityはRFC 3161タイムスタンプを発行するサービスです。バージョン2.0.5以下にはVerifyTimestampResponse関数に認可バイパスの脆弱性があります。VerifyTimestampResponseは証明書チェーンの署名を正しく検証しますが、VerifyLeafCert内のTSA固有の制約チェックでは、検証済みチェーンのリーフ証明書ではなくPKCS#7証明書バッグの最初の非CA証明書を使用しています。攻撃者は、権限のあるキーでメッセージが署名されている間に偽造証明書を証明書バッグの先頭に付加することで、この脆弱性を悪用できます。これにより、ライブラリは署名をある証明書に対して検証しつつ、認可チェックを別の証明書に対して行うことになります。この脆弱性はtimestamp-authority/v2/pkg/verificationパッケージの利用者のみが影響を受け、timestamp-authorityサービス自体やsigstore-goには影響を及ぼしません。この問題はバージョン2.0.6で修正されています。

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.
Fix availability varies by product
Affected
Fixed
2.0.6.
Action
Use the product-specific evidence above. Patch only products with a verified fixed release, and keep every affected or under-investigation state without a matching fix in the remediation queue.
Workaround
No verified workaround is recorded. Limit untrusted access and use least privilege until authoritative guidance is available.
04

Evidence and provenance

Published 14 Apr 2026 · Last source change 16 Apr 2026, 14:00 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-2026-22813
Product sourceVendor CSAF · SUSE Product Security Team
Remediation sourceVendor CSAF · SUSE Product Security Team
CWE sourceCNA
NVD statusNVD enriched

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

Material change intelligence

What changed after publication

View recent updates ↗

No material field changes have been recorded since change tracking began. Routine source refreshes and cosmetic edits are intentionally excluded.

Material fields only · duplicate refreshes suppressed · history retained for the configured operational retention period
CVE published
Fixed release or patch reference recorded
ENISA EUVD · EUVD-2026-22813↗Vendor CSAF · SUSE Product Security Team↗CVE authority or vendor reference · GitHub GHSA-XM5M-WGH2-RRG3↗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-2026-39984 · cve.blacktree.nl