Syntax-highlighting hang via zero-width state reentry
Published Mar 23, 2021 · Updated Aug 3, 2024
Infinite-loop denial of service in Pygments 1.5 through 2.7.3 allows attackers to hang syntax highlighting with crafted SML input. The SMLLexer zero-width lookahead for the exception keyword transitions back into the same lexer state without consuming input. Exploitation requires an application to submit attacker-controlled Standard ML text to SMLLexer; the affected highlighting operation hangs, consuming processor time without reported data exposure or modification.
Summary
What happened
Infinite-loop denial of service in Pygments 1.5 through 2.7.3 allows attackers to hang syntax highlighting with crafted SML input. The SMLLexer zero-width lookahead for the exception keyword transitions back into the same lexer state without consuming input. Exploitation requires an application to submit attacker-controlled Standard ML text to SMLLexer; the affected highlighting operation hangs, consuming processor time without reported data exposure or modification.
The record
- CVE
- CVE-2021-20270
- Published
- Mar 23, 2021
- Updated
- Aug 3, 2024
- Vendor
- Pygments
- Product
- Pygments
- Classifications
- CWE-835, T1499.004
- Attack vector
- network
- Privileges
- unauthenticated
Timeline
How it unfolded
- Mar 23, 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=python-pygments 2.7.4
What conditions does exploitation require?
What is affected?
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 SMLLexer exception-token reproducerproof of concept · demonstrated
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Technologies
Your stack
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Your stack
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