CRITICAL
CVE-2021-26691
CWE-122Published: June 10, 2021· Updated: Jun 17, 2026
9.8
CVSS v3.1
Official 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
Technical Analysis
CVE-2021-26691 can be exploited remotely over the network without requiring physical or adjacent access, significantly expanding the attack surface for threat actors.
The vulnerability requires no privileges and no user interaction, making it a prime target for automated exploitation campaigns and worm-like propagation.
A successful exploit results in complete confidentiality breach (data exposure), full integrity compromise (data manipulation), availability disruption (denial of service), with a CVSS base score of 9.8.
CVSS v3.1 Vector Breakdown
Exploitability
Attack VectorNetwork
Attack ComplexityLow
Privileges Req.None
User InteractionNone
ScopeUnchanged
Impact
ConfidentialityHigh
IntegrityHigh
AvailabilityHigh
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H
Affected Vendors & Products
Exploit & PoC Resources
NO KNOWN EXPLOITNo public exploit confirmed at this time
Exploit-DB
Offensive Security exploit database
GitHub PoC Search
Community PoC repositories
Rapid7 / Metasploit
Metasploit module search
PacketStorm
Security advisories & exploits
NVD Detail
Official NIST entry
MITRE CVE
CVE Program entry
External links open in a new tab. Always verify in a controlled environment before use.
Official Patches & Advisories
All References (26)
→
http://httpd.apache.org/security/vulnerabilities_24.htmlVendor Advisory
→
http://www.openwall.com/lists/oss-security/2021/06/10/7Mailing List · Third Party Advisory
→
https://lists.apache.org/thread.html/re026d3da9d7824bd93b9f871c0fdda978d960c7e62d8c43cba8d0bf3%40%3Ccvs.httpd.apache.org%3EMailing List · Release Notes · Vendor Advisory
→
https://lists.debian.org/debian-lts-announce/2021/07/msg00006.htmlMailing List · Third Party Advisory
→
https://security.gentoo.org/glsa/202107-38Third Party Advisory
→
https://security.netapp.com/advisory/ntap-20210702-0001/Third Party Advisory
→
https://www.debian.org/security/2021/dsa-4937Mailing List · Third Party Advisory
→
https://www.oracle.com/security-alerts/cpujan2022.htmlPatch · Third Party Advisory
→
https://www.oracle.com/security-alerts/cpuoct2021.htmlPatch · Third Party Advisory
→
http://httpd.apache.org/security/vulnerabilities_24.htmlVendor Advisory
→
http://www.openwall.com/lists/oss-security/2021/06/10/7Mailing List · Third Party Advisory
Quick Facts
CVE IDCVE-2021-26691
CVSS Score9.8 / 10
SeverityCRITICAL
WeaknessCWE-122
CISA KEVNo
Affected5 vendor(s)
PublishedJun 10, 2021
Related CVEs (CWE-122)
Recommended Actions
- →Apply vendor patches immediately
- →Monitor CVE-2021-26691 in threat intel feeds
- →Review IDS/IPS signatures for exploitation attempts
Data sourced from NVD (NIST), CISA KEV, and EPSS (FIRST). Analysis generated by CTIWatch. CVE data is provided under the NVD usage policy.