CVE-2021-26691
Apache HTTP Server mod_session response handling heap overflow
Description
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
Official description from the CVE record, published by apache. Copyright © 1999-2026 The MITRE Corporation. See /security/cve/legal for the CVE license. View the record on cve.org
Key data
EPSS
Exploit Prediction Scoring System by FIRST: an estimate of the probability that exploitation activity will be observed in the next 30 days.
- Score
- 0.68067 (68.1% probability)
- Percentile
- 99.3%
- Scores of
- Nov 10, 2026
- Model
- v2026.06.15
Weakness (CWE)
CWE catalog version 5.0.
CWE names: Copyright © 2006-2026, The MITRE Corporation. See /security/cve/legal for the CWE license.
- CWE-122Heap-based Buffer Overflow
Affected products
Products listed in the CVE record, as the CNA published them.
Apache HTTP Server
- affected: 2.4.46
- affected: 2.4.43
- affected: 2.4.41
- affected: 2.4.39
- affected: 2.4.38
- affected: 2.4.37
- affected: 2.4.35
- affected: 2.4.34
- affected: 2.4.33
- affected: 2.4.29
- affected: 2.4.28
- affected: 2.4.27
- affected: 2.4.26
- affected: 2.4.25
- affected: 2.4.23
- affected: 2.4.20
- affected: 2.4.18
- affected: 2.4.17
- affected: 2.4.16
- affected: 2.4.12
- affected: 2.4.10
- affected: 2.4.9
- affected: 2.4.7
- affected: 2.4.6
- affected: 2.4.4
- and 4 more
References
Links listed in the CVE record. They lead to other sites, which CubePath does not control.
- httpd.apache.org/security/vulnerabilities_24.html
- lists.apache.org/thread.html/re026d3da9d7824bd93b9f871c0fdd…
- [httpd-announce] 20210609 CVE-2021-26691: mod_session response handling heap overflow (lists.apache.org)mailing-list
- [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-2021-26690.json CVE-2021-26691.json CVE-2021-30641.json CVE-2021-31618.json (lists.apache.org)mailing-list
- [oss-security] 20210609 CVE-2021-26691: Apache httpd: mod_session response handling heap overflow (openwall.com)mailing-list
- [debian-lts-announce] 20210709 [SECURITY] [DLA 2706-1] apache2 security update (lists.debian.org)mailing-list
- DSA-4937 (debian.org)vendor-advisory
- GLSA-202107-38 (security.gentoo.org)vendor-advisory
- FEDORA-2021-dce7e7738e (lists.fedoraproject.org)vendor-advisory
- FEDORA-2021-e3f6dd670d (lists.fedoraproject.org)vendor-advisory
- oracle.com/security-alerts/cpuoct2021.html
- security.netapp.com/advisory/ntap-20210702-0001
- oracle.com/security-alerts/cpujan2022.html
Timeline
- ID reserved
- Record published
- Record last updated
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About CubePath
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Data from the CVE Program (MITRE), CISA KEV and FIRST EPSS. CVSS is owned by FIRST and used by permission. Not affiliated with or endorsed by MITRE, CISA or FIRST. Data as of Nov 10, 2026, 19:53 UTC. Sources and licenses