Client crash via malformed authentication header
Published Jan 17, 2023 · Updated Dec 22, 2025
Regular expression denial of service in Mechanize before 0.4.6 allows remote attackers to crash clients through a malicious HTTP response. AbstractBasicAuthHandler applies a backtracking regular expression to an untrusted WWW-Authenticate header whose comma-heavy form triggers excessive processing. The client must request an attacker-controlled server and process its authentication challenge; exploitation crashes only the consuming process.
Summary
What happened
Regular expression denial of service in Mechanize before 0.4.6 allows remote attackers to crash clients through a malicious HTTP response. AbstractBasicAuthHandler applies a backtracking regular expression to an untrusted WWW-Authenticate header whose comma-heavy form triggers excessive processing. The client must request an attacker-controlled server and process its authentication challenge; exploitation crashes only the consuming process.
The record
- CVE
- CVE-2021-32837
- Published
- Jan 17, 2023
- Updated
- Dec 22, 2025
- Vendor
- python-mechanize
- Product
- Mechanize
- Classifications
- CWE-1333, T1499.004
- Attack vector
- network
- Privileges
- unauthenticated
Timeline
How it unfolded
- Jan 17, 2023CVE publishedPublication date reported by the CVE source.
- Dec 22, 2025Record 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=0.4.6 <0.4.6
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.
Weakness, pattern, technique
Public exploit references
- Malicious WWW-Authenticate header reproductionproof of concept · demonstrated
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Technologies
Your stack
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Your stack
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