Service interruption via tag-attribute regex backtracking
Published Sep 7, 2022 · Updated Dec 3, 2025
Regular expression denial of service in SQLAlchemy Mako before 1.2.2 allows remote attackers to interrupt services via crafted templates. In Lexer.match_tag_start, the tag-attribute regex treats quoted sections as permissive wildcard matches, causing excessive backtracking on tags containing thousands of quote characters. Exploitation requires an application or extraction plugin to pass attacker-controlled template text to Lexer.parse, resulting in CPU exhaustion that stalls template processing.
Summary
What happened
Regular expression denial of service in SQLAlchemy Mako before 1.2.2 allows remote attackers to interrupt services via crafted templates. In Lexer.match_tag_start, the tag-attribute regex treats quoted sections as permissive wildcard matches, causing excessive backtracking on tags containing thousands of quote characters. Exploitation requires an application or extraction plugin to pass attacker-controlled template text to Lexer.parse, resulting in CPU exhaustion that stalls template processing.
The record
- CVE
- CVE-2022-40023
- Published
- Sep 7, 2022
- Updated
- Dec 3, 2025
- Vendor
- Unknown vendor
- Product
- Unknown product
- Classifications
- CWE-1333, CAPEC-492, T1499.004
- Attack vector
- network
- Privileges
- unauthenticated
Timeline
How it unfolded
- Sep 7, 2022CVE publishedPublication date reported by the CVE source.
- Dec 3, 2025Record updatedLatest update available in the CVE record.
Exploitability
Present is not the same as exploitable
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What conditions does exploitation require?
What is affected?
Affected products and versions are unavailable in this record.
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
- Upstream 3,000-quote Lexer regression triggerproof of concept · demonstrated
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Technologies
Your stack
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Your stack
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