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CVE-2021-26691— Apache HTTP Server mod_session response handling heap overflow

Quick assessment

Affected

Apache Software Foundation Apache HTTP Server

Exploitation

Public or AI PoC available; prioritize validation

Recommended action

Check the vendor advisory and references for a fixed version. If immediate upgrade is impossible, restrict exposure and increase monitoring.

Apache HTTP Server是美国阿帕奇（Apache）基金会的一款开源网页服务器。该服务器具有快速、可靠且可通过简单的API进行扩充的特点。 Apache HTTP Server 2.4.0 to 2.4.46存在缓冲区错误漏洞，该漏洞允许远程攻击者可利用该漏洞执行拒绝服务(DoS)攻击。

AI Predicted 7.5 Difficulty: Easy EPSS 68.29% · P99 Updated Feb 25, 2026

Possible ATT&CK Techniques 1 AI

T1190 · Exploit Public-Facing Application

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I. Basic Information for CVE-2021-26691

Vulnerability Information

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Vulnerability Title

Apache HTTP Server mod_session response handling heap overflow

Source: CVE Program / CVE List V5

Vulnerability 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

Source: CVE Program / CVE List V5

CVSS Information

N/A

Source: CVE Program / CVE List V5

Vulnerability Type

堆缓冲区溢出

Source: CVE Program / CVE List V5

Vulnerability Title

Apache HTTP Server 缓冲区错误漏洞

Source: CNNVD (China National Vulnerability Database)

Vulnerability Description

Source: CNNVD (China National Vulnerability Database)

CVSS Information

N/A

Source: CNNVD (China National Vulnerability Database)

Vulnerability Type

N/A

Source: CNNVD (China National Vulnerability Database)

Affected Products

Vendor	Product	Affected Versions	CPE	Subscribe
Apache Software Foundation	Apache HTTP Server	2.4.46	-

II. Public POCs for CVE-2021-26691

#	POC Description	Source Link	Shenlong Link
1	None	https://github.com/dja2TaqkGEEfA45/CVE-2021-26691	POC Details

AI-Generated POC Premium

No public POC found.

III. Intelligence Information for CVE-2021-26691

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Vendor Advisories for CVE-2021-26691 (6)

https://www.oracle.com/security-alerts/cpujan2022.html x_refsource_MISC
https://www.oracle.com/security-alerts/cpuoct2021.html x_refsource_MISC
http://httpd.apache.org/security/vulnerabilities_24.html x_refsource_MISC
https://security.netapp.com/advisory/ntap-20210702-0001/ x_refsource_CONFIRM
https://www.debian.org/security/2021/dsa-4937 vendor-advisory x_refsource_DEBIAN
https://security.gentoo.org/glsa/202107-38 vendor-advisory x_refsource_GENTOO

Mailing List Discussions for CVE-2021-26691 (6)

https://lists.apache.org/thread.html/re026d3da9d7824bd93b9f871c0fdda978d960c7e62d8c43cba8d0bf3%40%3Ccvs.httpd.apache.org%3E x_refsource_MISC
https://lists.fedoraproject.org/archives/list/package-announce%40lists.fedoraproject.org/message/ZNCYSR3BXT36FFF4XTCPL3HDQK4VP45R/ vendor-advisory x_refsource_FEDORA
https://lists.fedoraproject.org/archives/list/package-announce%40lists.fedoraproject.org/message/SPBR6WUYBJNACHKE65SPL7TJOHX7RHWD/ vendor-advisory x_refsource_FEDORA
https://lists.debian.org/debian-lts-announce/2021/07/msg00006.html mailing-list x_refsource_MLIST
http://www.openwall.com/lists/oss-security/2021/06/10/7 mailing-list x_refsource_MLIST
https://lists.apache.org/thread.html/r7f2b70b621651548f4b6f027552f1dd91705d7111bb5d15cda0a68dd%40%3Cdev.httpd.apache.org%3E mailing-list x_refsource_MLIST

https://www.cve.org/CVERecord?id=CVE-2021-26691

Same Patch Batch · Apache Software Foundation · 2021-06-10 · 7 CVEs total

CVE-2021-30641		Unexpected URL matching with 'MergeSlashes OFF'
CVE-2021-26690		mod_session NULL pointer dereference
CVE-2020-13950		mod_proxy_http NULL pointer dereference
CVE-2020-35452		mod_auth_digest possible stack overflow by one nul byte
CVE-2020-13938		Improper Handling of Insufficient Privileges
CVE-2019-17567		mod_proxy_wstunnel tunneling of non Upgraded connections

IV. Related Vulnerabilities

Same product: Apache HTTP Server

Same vendor: Apache Software Foundation

Same weakness: CWE-122

V. Comments for CVE-2021-26691

No comments yet

Goal Reached Thanks to every supporter — we hit 100%!

CVE-2021-26691— Apache HTTP Server mod_session response handling heap overflow

Quick assessment

Possible ATT&CK Techniques 1 AI

I. Basic Information for CVE-2021-26691

Vulnerability Information

Vulnerability Title

Vulnerability Description

CVSS Information

Vulnerability Type

Vulnerability Title

Vulnerability Description

CVSS Information

Vulnerability Type

Affected Products

II. Public POCs for CVE-2021-26691

III. Intelligence Information for CVE-2021-26691

Vendor Advisories for CVE-2021-26691 (6)

Mailing List Discussions for CVE-2021-26691 (6)

Same Patch Batch · Apache Software Foundation · 2021-06-10 · 7 CVEs total

IV. Related Vulnerabilities

V. Comments for CVE-2021-26691

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