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Full vulnerability report · 2021
CVE-2021-26690High confidence

mod_session NULL pointer dereference

Apache Software Foundation · Apache HTTP Server

7.5HighCVSS 3.1
Recommended action
Within 7 days

High technical severity; prioritise exposed affected systems while verifying vendor guidance.

Patch available
R
Operational reassessment

Published severity in operational context

Open reassessment dashboard →
Published severityHighOperational priority:Critical, raised one band.upgradedsince 5 Oct 2026

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 65.31% 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 Apache Software Foundation Apache HTTP Server 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: Within 3 daysRemediation target: Within 90 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

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

7 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
Alpine v3.23v3.23 · mainapache2Vendor fix publishedAlpine records a security fix at this version. An absent entry does not mean the package is unaffected.2.4.48-r0Alpine Security Database ↗Source updated 3 Oct 2026
Alpine v3.22v3.22 · mainapache2Vendor fix publishedAlpine records a security fix at this version. An absent entry does not mean the package is unaffected.2.4.48-r0Alpine Security Database ↗Source updated 3 Oct 2026
Alpine v3.21v3.21 · mainapache2Vendor fix publishedAlpine records a security fix at this version. An absent entry does not mean the package is unaffected.2.4.48-r0Alpine Security Database ↗Source updated 3 Oct 2026
Debian trixietrixie · sourceapache2Vendor fix publishedDebian records a fixed source-package version for this release.2.4.46-6Debian Security Tracker ↗Source updated 5 Oct 2026
Debian bookwormbookworm · sourceapache2Vendor fix publishedDebian records a fixed source-package version for this release.2.4.46-6Debian Security Tracker ↗Source updated 5 Oct 2026
Debian forkyforky · sourceapache2Vendor fix publishedDebian records a fixed source-package version for this release.2.4.46-6Debian Security Tracker ↗Source updated 5 Oct 2026
Debian sidsid · sourceapache2Vendor fix publishedDebian records a fixed source-package version for this release.2.4.46-6Debian Security Tracker ↗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-2021-26690 · CSAF 2.0 · revision 3 · finalRed Hat Product Securityhttpd: mod_session: NULL pointer dereference when parsing Cookie header
21 known affected

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

  • httpd as a component of Red Hat Enterprise Linux 7
  • httpd-devel as a component of Red Hat Enterprise Linux 7
  • httpd-manual as a component of Red Hat Enterprise Linux 7
  • httpd-tools as a component of Red Hat Enterprise Linux 7
  • httpd.src as a component of Red Hat Enterprise Linux 7
  • mod_ldap as a component of Red Hat Enterprise Linux 7
  • mod_proxy_html as a component of Red Hat Enterprise Linux 7
  • mod_session as a component of Red Hat Enterprise Linux 7
  • mod_ssl as a component of Red Hat Enterprise Linux 7
  • httpd22 as a component of Red Hat JBoss Enterprise Application Platform 6
  • httpd22 as a component of Red Hat JBoss Enterprise Web Server 2
  • httpd24-httpd as a component of Red Hat Software Collections
Summary
A NULL pointer dereference was found in Apache httpd mod_session. The highest threat from this vulnerability is to system availability.
Remediation
Before applying this update, make sure all previously released errata relevant to your system have been applied. For details on how to apply this update, refer to: https://access.redhat.com/articles/11258
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-2021-13483

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 actionWithin 7 days

High technical severity; prioritise exposed affected systems while verifying vendor guidance.

Patch available
01

What, why and how

Apache HTTP Server versions 2.4.0 to 2.4.46 A specially crafted Cookie header handled by mod_session can cause a NULL pointer dereference and crash, leading to a possible Denial Of Service

What

Apache HTTP Server versions 2.4.0 to 2.4.46 A specially crafted Cookie header handled by mod_session can cause a NULL pointer dereference and crash, leading to a possible Denial Of Service

Why

The product dereferences a pointer that it expects to be valid but is NULL.

How

An attacker operating through a network path may attempt exploitation without authentication or user interaction. If successful, the issue may disrupt the affected service.

What

Apache HTTP Server versions 2.4.0 to 2.4.46 A specially crafted Cookie header handled by mod_session can cause a NULL pointer dereference and crash, leading to a possible Denial Of Service

Why

The product dereferences a pointer that it expects to be valid but is NULL.

How

An attacker operating through a network path may attempt exploitation without authentication or user interaction. If successful, the issue may disrupt the affected service.

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 → NULL Pointer Dereference → disrupt the affected service
Attack surface
Network
Privileges required
None: unauthenticated exploitation is possible
User interaction
None
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-476 ↗

CWE-476: NULL Pointer Dereference. The product dereferences a pointer that it expects to be valid but is NULL.

CVSS vector
?CVSS means Common Vulnerability Scoring System. The vector records the metric values used to calculate technical severity.
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H

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

AVNetworkAttack vector: The vulnerable component can be reached over a network.ACLowAttack complexity: No specialised conditions are required beyond attacker-controlled input.PRNonePrivileges required: The attacker does not need an account or existing privileges.UINoneUser interaction: No action by another user is required.SUnchangedScope: The security impact remains within the vulnerable component's authority.CNoneConfidentiality impact: No direct loss is represented by this metric.INoneIntegrity impact: No direct loss is represented by this metric.AHighAvailability impact: A successful attack can cause a major loss.
Post-exploitation / living off the land
No specific living-off-the-land technique is confirmed in the structured sources. Monitor normal administration tools for activity inconsistent with the affected service's baseline.
NetworkUnauthenticatedDenial of serviceCWE-476
A

Official authority intelligence

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

BSI · German · WID-SEC-2022-0438Apache HTTP Server: Mehrere Schwachstellen

Ein entfernter, anonymer Angreifer kann mehrere Schwachstellen in Apache HTTP Server ausnutzen, um einen Denial of Service Angriff durchzuführen, Sicherheitsvorkehrungen zu umgehen oder sonstige Auswirkungen zu verursachen.

Official advisory ↗
BSI · German · WID-SEC-2024-1591Juniper JUNOS: Mehrere Schwachstellen

Ein Angreifer kann mehrere Schwachstellen in Juniper JUNOS ausnutzen, um einen Denial of Service zu verursachen, Informationen offenzulegen, Privilegien zu erweitern und Sicherheitsmechanismen inklusive zu umgehen.

Official advisory ↗
Cyber Security Agency of Singapore · English · CSA-SB-20210616Security Bulletin 16 Jun 2021

The Cyber Security Agency of Singapore included this CVE in its official Security Bulletin 16 Jun 2021, published on 16 June 2021. Open the linked bulletin for the product, severity and reference information published in that issue.

Official advisory ↗
CERT-FR · French · CERTFR-2024-AVI-0575Multiples vulnérabilités dans les produits Juniper Networks

.org/CVERecord?id=CVE-2020-9490 Référence CVE CVE-2021-22543 https://www.cve.org/CVERecord?id=CVE-2021-22543 Référence CVE CVE-2021-2342 https://www.cve.org/CVERecord?id=CVE-2021-2342 Référence CVE CVE-2021-23440 https://www.cve.org/CVERecord?id=CVE-2021-23440 Référence CVE CVE-2021-2356 https://www.cve.org/CVERecord?id=CVE-2021-2356 Référence CVE CVE-2021-2372 https://www.cve.org/CVERecord?id=CVE-2021-2372 Référence CVE CVE-2021-2385 https://www.cve.org/CVERecord?id=CVE-2021-2385 Référence CVE CVE-2021-2389 https://www.cve.org/CVERecord?id=CVE-2021-2389 Référence CVE CVE-2021-2390 https://www.cve.org/CVERecord?id=CVE-2021-2390 Référence CVE CVE-2021-26690 https://www.cve.org/CVERecord?id=CVE-2021-26690 Référence CVE CVE-2021-26691 https://www.cve.org/CVERecord?id=CVE-2021-26691 Référence CVE CVE-2021-27290 https://www.cve.org/CVERecord?id=CVE-2021-27290 Référence CVE CVE-2021-29469 https://www.cve.org/CVERecord?id=CVE-2021-29469 Référence CVE CVE-2021-30641 https://www.cve.org/CVERecord?id=CVE-2021-30641 Référence CVE CVE-2021-31535 https://www.cve.org/CVERecord?id=CVE-2021-31535 Référence CVE CVE-2021-31618 https://www.cve.org/CVERecord?id=CVE-2021-31618 Référence CVE CVE-2021-3177 https://www.cve.org/CVERecord?id=CVE-2021-3177 Référence CVE CVE-2021-32803 https://www.cve.org/CVERecord?id=CV

Official advisory ↗
CERT-FR · French · CERTFR-2021-AVI-875Multiples vulnérabilités dans les produits Check Point

De multiples vulnérabilités ont été découvertes dans les produits Check Point. Certaines d'entre elles permettent à un attaquant de provoquer un déni de service à distance, un contournement de la politique de sécurité et une atteinte à l'intégrité des données.

Official advisory ↗
JVN iPedia · Japanese · JVNDB-2021-008068Apache HTTP Server におけるヒープオーバーフローの脆弱性

Apache HTTP Server には、ヒープオーバーフローの脆弱性が存在します。

Official advisory ↗
JVN iPedia · Japanese · JVNDB-2021-008067Apache HTTP Server の mod_session における NULL ポインタデリファレンスに関する脆弱性

Apache HTTP Server の mod_session には、NULL ポインタデリファレンスおよびクラッシュサービス運用妨害 (DoS) 状態にされる脆弱性が存在します。

Official advisory ↗
JVN iPedia · Japanese · JVNDB-2020-016881Apache HTTP Server の mod_proxy_http における NULL ポインタデリファレンスに関する脆弱性

Apache HTTP Server の mod_proxy_http には、NULL ポインタデリファレンスに関する脆弱性が存在します。

Official advisory ↗
JVN iPedia · Japanese · JVNDB-2020-016879Apache HTTP Server の mod_auth_digest におけるスタックオーバーフローの脆弱性

Apache HTTP Server の mod_auth_digest には、スタックオーバーフローの脆弱性が存在します。

Official advisory ↗
JVN iPedia · Japanese · JVNDB-2021-012709Apache HTTP Server における 'MergeSlashes OFF' の予期しないマッチング動作に関する脆弱性

Apache HTTP Server には、'MergeSlashes OFF' の予期しないマッチング動作に関する脆弱性が存在します。

Official advisory ↗
JVN iPedia · Japanese · JVNDB-2019-016322Apache HTTP Server の mod_proxy_wstunnel における HTTP リクエストスマグリングに関する脆弱性

Apache HTTP Server の mod_proxy_wstunnel には、オリジンサーバによりアップグレードされない URL が設定された際、接続全体をトンネリングしているため、HTTP リクエストスマグリングに関する脆弱性が存在します。

Official advisory ↗
JVN iPedia · Japanese · JVNDB-2021-007327Apache HTTP Server における Windows 上で稼働する httpd を停止される脆弱性

Apache HTTP Server には、Windows 上で稼働する httpd を停止される脆弱性が存在します。

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
Fixed
Action
Before applying this update, make sure all previously released errata relevant to your system have been applied. For details on how to apply this update, refer to: https://access.redhat.com/articles/11258
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 10 Jun 2021 · Last source change 3 Aug 2024, 20:33 UTC · CWE-476 · NULL Pointer Dereference

CVE recordCVE.org · 5.1
CVSS sourceNIST NVD
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-2021-13483
Product sourceVendor CSAF · Red Hat Product Security
Remediation sourceVendor CSAF · Red Hat Product Security
CWE sourceNIST NVD
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
    2.4.46; 2.4.43; 2.4.41; 2.4.39; 2.4.38; 2.4.37; 2.4.35; 2.4.34 · Fixed: No fixed version is explicitly recorded in the structured CVE data.
    After
    2.4.46; 2.4.43; 2.4.41; 2.4.39; 2.4.38; 2.4.37; 2.4.35; 2.4.34 · Fixed: Before applying this update, make sure all previously released errata relevant to your system have been applied. For details on how to apply this update, refer to: https://access.redhat.com/articles/11258
    Red Hat Product Security ↗
  2. Remediation statusRemediation status changed from Awaiting fix to Patch available.
    Before
    Awaiting fix
    After
    Patch available
    Red Hat Product Security ↗
Material fields only · duplicate refreshes suppressed · history retained for the configured operational retention period
CVE published
Fixed release recorded from official guidance
ENISA EUVD · EUVD-2021-13483↗Red Hat Product Security security advisory↗CVE authority or vendor reference↗Vendor advisory↗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-2021-26690 · cve.blacktree.nl