Parsing interruption via uncounted Any recursion
Published Jan 23, 2026 · Updated Jan 23, 2026
Uncontrolled recursion in Python Protocol Buffers before 5.29.6 and 6.30.0rc1 through 6.33.4 allows attackers to interrupt parsing. _ConvertAnyMessage() recursively invokes itself through methodcaller() for nested well-known types instead of returning through ConvertMessage(), so max_recursion_depth is not decremented and deeply nested google.protobuf.Any objects exhaust Python's recursion stack. Reachability requires an application to pass attacker-influenced nested Any JSON dictionaries to google.protobuf.json_format.ParseDict; the bounded consequence is a RecursionError that interrupts the parsing process.
Summary
What happened
Uncontrolled recursion in Python Protocol Buffers before 5.29.6 and 6.30.0rc1 through 6.33.4 allows attackers to interrupt parsing. _ConvertAnyMessage() recursively invokes itself through methodcaller() for nested well-known types instead of returning through ConvertMessage(), so max_recursion_depth is not decremented and deeply nested google.protobuf.Any objects exhaust Python's recursion stack. Reachability requires an application to pass attacker-influenced nested Any JSON dictionaries to google.protobuf.json_format.ParseDict; the bounded consequence is a RecursionError that interrupts the parsing process.
The record
- CVE
- CVE-2026-0994
- Published
- Jan 23, 2026
- Updated
- Jan 23, 2026
- Vendor
- Go standard library
- Product
- Protocol Buffers
- Classifications
- CWE-674, T1499.004
- Attack vector
- network
- Privileges
- unauthenticated
Timeline
How it unfolded
- Jan 23, 2026CVE publishedPublication date reported by the CVE source.
- Jan 23, 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=>= V33.0
What conditions does exploitation require?
What is affected?
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
- Any JSON recursion depth bypass reproductionproof of concept · demonstrated
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Technologies
Your stack
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Your stack
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