CPU exhaustion via quadratic CSV regex backtracking
Published Aug 10, 2026 · Updated Aug 10, 2026
Inefficient CPU computation in CPython's csv module allows local users to cause a prolonged hang with attacker-controlled CSV samples. The _guess_quote_and_delimiter heuristics apply backtracking regular expressions whose work grows quadratically on quoted input. Reachability requires an application to pass unbounded, attacker-influenced data to csv.Sniffer.sniff(); confidentiality and integrity remain unaffected.
Summary
What happened
Inefficient CPU computation in CPython's csv module allows local users to cause a prolonged hang with attacker-controlled CSV samples. The _guess_quote_and_delimiter heuristics apply backtracking regular expressions whose work grows quadratically on quoted input. Reachability requires an application to pass unbounded, attacker-influenced data to csv.Sniffer.sniff(); confidentiality and integrity remain unaffected.
The record
- CVE
- CVE-2026-18503
- Published
- Aug 10, 2026
- Updated
- Aug 10, 2026
- Vendor
- Python Software Foundation
- Product
- CPython
- Classifications
- CWE-1176, T1499.004
- Attack vector
- local
- Privileges
- authenticated
Timeline
How it unfolded
- Aug 10, 2026CVE publishedPublication date reported by the CVE source.
- Aug 10, 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?
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- Affected versionversion=0 <3.13.15
- Affected versionversion=3.14.0 <3.14.7
- Affected versionversion=3.15.0a1 <3.15.0rc1
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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