Remote denial of service via malformed session cookie
Published Jun 10, 2021 · Updated Aug 3, 2024
Denial of service in mod_session in Apache HTTP Server 2.4.0 through 2.4.46 allows remote attackers to crash workers via a Cookie header. In session_identity_decode(), the parser calls apr_strtok() again even when the first tokenization yields no key, allowing a malformed pair to reach a NULL dereference. Reachability requires mod_session, an enabled session, and a client-stored session cookie; each successful request interrupts an httpd worker.
Summary
What happened
Denial of service in mod_session in Apache HTTP Server 2.4.0 through 2.4.46 allows remote attackers to crash workers via a Cookie header. In session_identity_decode(), the parser calls apr_strtok() again even when the first tokenization yields no key, allowing a malformed pair to reach a NULL dereference. Reachability requires mod_session, an enabled session, and a client-stored session cookie; each successful request interrupts an httpd worker.
The record
- CVE
- CVE-2021-26690
- Published
- Jun 10, 2021
- Updated
- Aug 3, 2024
- Vendor
- The Apache Software Foundation
- Product
- Apache HTTP Server
- Classifications
- CWE-476, T1499
- Attack vector
- network
- Privileges
- unauthenticated
Timeline
How it unfolded
- Jun 10, 2021CVE publishedPublication date reported by the CVE source.
- Aug 3, 2024Record updatedLatest update available in the CVE record.
Exploitability
Present is not the same as exploitable
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Is a vulnerable build present?
Compare these published version ranges with your installed build and any vendor patches.
- Affected versionversion=2.4.0
- Affected versionversion=2.4.1
- Affected versionversion=2.4.10
- Affected versionversion=2.4.12
- Affected versionversion=2.4.16
- Affected versionversion=2.4.17
- Affected versionversion=2.4.18
- Affected versionversion=2.4.2
- Affected versionversion=2.4.20
- Affected versionversion=2.4.23
- Affected versionversion=2.4.25
- Affected versionversion=2.4.26
- Affected versionversion=2.4.27
- Affected versionversion=2.4.28
- Affected versionversion=2.4.29
- Affected versionversion=2.4.3
- Affected versionversion=2.4.33
- Affected versionversion=2.4.34
- Affected versionversion=2.4.35
- Affected versionversion=2.4.37
- Affected versionversion=2.4.38
- Affected versionversion=2.4.39
- Affected versionversion=2.4.4
- Affected versionversion=2.4.41
- Affected versionversion=2.4.43
- Affected versionversion=2.4.46
- Affected versionversion=2.4.6
- Affected versionversion=2.4.7
- Affected versionversion=2.4.9
What conditions does exploitation require?
What is affected?
Published CVSS scores
CVSS describes severity. EPSS estimates exploitation probability.
Attacks
What attackers are doing with it
Daily unique IPs observed by Shadowserver honeypots for known exploited vulnerabilities (KEVs). Missing observations do not establish an absence of attacks.
Public exploit references
- CVE-2021-26690 Apache mod_session proof of conceptproof of concept · unverified
Labels summarize the accepted research assessment. They do not indicate a test against your environment.
Technologies
Your stack
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Your stack
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