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Vulnerability record · public intelligence
CVE-2021-26691
UNKNOWN

Apache HTTP Server mod_session response handling heap overflow

Published Jun 10, 2021 · Updated Nov 3, 2026

Severity · CVSSUNKNOWN · Not scored
Known exploitationNot listed
EPSS / likelihood68.29%
QFinch risk scoreNot available

Original summary

Normalized public record · Updated Nov 3, 2026

Apache HTTP Server mod_session response handling heap overflow

Publisher and source text is retained separately from QFinch interpretation.

QFinch assessment

In Apache HTTP Server versions 2.4.0 to 2.4.46 a specially crafted SessionHeader sent by an origin server could cause a heap overflow

Evidence: public source records

Affected products

Affected scope reported by the available public evidence
Affected package, product or rangeFix status
Consult the referenced vendor advisory for affected versions.Consult source advisory

Matching a version is only one part of assessing exposure. QFinch has not assessed your environment on this public page.

Remediation

Apply the vendor-supported fixed release or mitigation, then verify the affected component is no longer reachable.

  1. Confirm the affected product and reachable code path exist in your environment.
  2. Apply the vendor-supported patch or mitigation from the primary advisory.
  3. Rescan the exact deployed revision and retain verification evidence.
Review primary references

Evidence coverage

FIRST-EPSSCVE-LIST-V5
SSVC priority
MEDIUM
Confidence
Not available
Aliases
None reported

Scores appear only when corresponding evidence exists. Missing data is never interpreted as zero risk.

Sources and record history

  1. httpd.apache.org ↗
  2. lists.apache.org ↗
  3. [httpd-announce] 20210609 CVE-2021-26691: mod_session response handling heap overflow ↗
  4. [httpd-dev] 20210610 Re: svn commit: r1890598 - in /httpd/site/trunk/content/security/json: CVE-2019-17567.json CVE-2020-13938.json CVE-2020-13950.json CVE-2020-35452.json CVE-2021 ↗
  5. [oss-security] 20210609 CVE-2021-26691: Apache httpd: mod_session response handling heap overflow ↗
  6. [debian-lts-announce] 20210709 [SECURITY] [DLA 2706-1] apache2 security update ↗
  7. DSA-4937 ↗
  8. GLSA-202107-38 ↗
  9. FEDORA-2021-dce7e7738e ↗
  10. FEDORA-2021-e3f6dd670d ↗
  11. www.oracle.com ↗
  12. security.netapp.com ↗

Record history

Published Jun 10, 2021 · Last refreshed Nov 3, 2026

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