Service interruption via quadratic end-of-file parsing
Published Jun 17, 2025 · Updated Jul 31, 2026
Algorithmic complexity in CPython HTMLParser allows remote authenticated users to interrupt services with crafted malformed HTML. The goahead end-of-file path rescans retained incomplete tags, comments, and declarations instead of closing or ignoring them, producing quadratic CPU work. Exposure requires an application to pass attacker-controlled malformed HTML to HTMLParser; the bounded consequence is excessive processing that interrupts that service.
Summary
What happened
Algorithmic complexity in CPython HTMLParser allows remote authenticated users to interrupt services with crafted malformed HTML. The goahead end-of-file path rescans retained incomplete tags, comments, and declarations instead of closing or ignoring them, producing quadratic CPU work. Exposure requires an application to pass attacker-controlled malformed HTML to HTMLParser; the bounded consequence is excessive processing that interrupts that service.
The record
- CVE
- CVE-2025-6069
- Published
- Jun 17, 2025
- Updated
- Jul 31, 2026
- Vendor
- Python Software Foundation
- Product
- CPython
- Classifications
- CWE-1333, T1499.004
- Attack vector
- network
- Privileges
- authenticated
Timeline
How it unfolded
- Jun 17, 2025CVE publishedPublication date reported by the CVE source.
- Jul 31, 2026Record 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 <3.9.24
- Affected versionversion=3.10.0 <3.10.19
- Affected versionversion=3.11.0 <3.11.14
- Affected versionversion=3.12.0 <3.12.12
- Affected versionversion=3.13.0 <3.13.6
- Affected versionversion=3.14.0a1 <3.14.0b3
What conditions does exploitation require?
What is affected?
Published CVSS scores
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Attacks
What attackers are doing with it
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Weakness, pattern, technique
Public exploit references
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Technologies
Your stack
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Your stack
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