Service interruption via unchecked lengths and recursion
Published Apr 16, 2026 · Updated Apr 16, 2026
Improper input validation in Google Protocol Buffers PHP Extension allows remote attackers to hang or crash parsing applications. CodedInputStream::readRaw accepts negative lengths decoded from varints, while its recursion counter writes to the wrong variable, bypassing the depth guard. Exploitation requires an application to parse attacker-supplied protobuf data; affected releases can loop, exhaust PHP workers, or crash.
Summary
What happened
Improper input validation in Google Protocol Buffers PHP Extension allows remote attackers to hang or crash parsing applications. CodedInputStream::readRaw accepts negative lengths decoded from varints, while its recursion counter writes to the wrong variable, bypassing the depth guard. Exploitation requires an application to parse attacker-supplied protobuf data; affected releases can loop, exhaust PHP workers, or crash.
The record
- CVE
- CVE-2026-6409
- Published
- Apr 16, 2026
- Updated
- Apr 16, 2026
- Vendor
- Go standard library
- Product
- Protocol Buffers PHP Extension
- Classifications
- CWE-20, CWE-400, T1499
- Attack vector
- network
- Privileges
- unauthenticated
Timeline
How it unfolded
- Apr 16, 2026CVE publishedPublication date reported by the CVE source.
- Apr 16, 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=0 <4.33.6
- Affected versionversion=0 <5.34.0-RC1
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
- Recursion-limit bypass reproductionproof of concept · demonstrated
- Negative-varint mergeFromString reproductionproof of concept · demonstrated
Labels summarize the accepted research assessment. They do not indicate a test against your environment.
Technologies
Your stack
See the directory against your own environment.
Your stack
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