Denial of service via next_inline infinite loop
Published Jan 20, 2023 · Updated Apr 2, 2025
Infinite-loop denial of service in Berkeley Yacc before 1.9.20200330 and 2.0 before 2.0.20210808 allows local users to hang parser generation. During more_curly() parsing, next_inline() enters a loop that never reaches an exit condition while processing the triggering file; the exact input sequence and faulty loop-control operation are not publicly disclosed. Exploitation requires user interaction with a local input file and hangs the parser-generation process, with no reported confidentiality or integrity impact.
Summary
What happened
Infinite-loop denial of service in Berkeley Yacc before 1.9.20200330 and 2.0 before 2.0.20210808 allows local users to hang parser generation. During more_curly() parsing, next_inline() enters a loop that never reaches an exit condition while processing the triggering file; the exact input sequence and faulty loop-control operation are not publicly disclosed. Exploitation requires user interaction with a local input file and hangs the parser-generation process, with no reported confidentiality or integrity impact.
The record
- CVE
- CVE-2021-33642
- Published
- Jan 20, 2023
- Updated
- Apr 2, 2025
- Vendor
- Thomas E. Dickey
- Product
- Berkeley Yacc (BYACC)
- Classifications
- CWE-835, T1499
- Attack vector
- local
- Privileges
- unauthenticated
Timeline
How it unfolded
- Jan 20, 2023CVE publishedPublication date reported by the CVE source.
- Apr 2, 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=<1.9.20200330 and <2.0.20210808
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
No public exploit references are available in this record.
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Technologies
Your stack
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Your stack
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