CVE-2026-6409
Official description Straight from the sourceThe vendor's or NVD's own wording, published unedited. Authoritative, but often terse — it says what broke, rarely what to do.
NVD · uneditedA Denial of Service (DoS) vulnerability exists in the Protobuf PHP library during the parsing of untrusted input. Maliciously structured messages—specifically those containing negative varints or deep recursion—can be used to crash the application, impacting service availability.
Technical summary Written by usOur analysis, written from the advisory, the CVSS vector and the affected-version data. It adds context the advisory leaves out, and never invents facts that are not in the source.
dbcve analysis · moderate confidenceThe Protobuf PHP library contains a denial-of-service vulnerability in its parsing logic. When parsing untrusted protobuf messages containing negative varints or those that trigger deep recursion, the parser can be induced to crash, causing the PHP application to terminate unexpectedly and impact service availability.
Verify against the referenced sources before acting — the references below are authoritative for this CVE, this summary is not.
CVSS breakdown How the score is builtThe industry scoring standard. It rates how the flaw is reached, what it takes to exploit, and what an attacker gains — the score is derived from those, not the other way round.
From the vector- Attack vector
- Network
- Complexity
- Low
- Privileges
- None
- Authentication
- X
- User interaction
- P
- Scope
- X
CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:P/VC:N/VI:N/VA:H/SC:N/SI:N/SA:N/E:X/CR:X/IR:X/AR:X/MAV:X/MAC:X/MAT:X/MPR:X/MUI:X/MVC:X/MVI:X/MVA:X/MSC:X/MSI:X/MSA:X/S:X/AU:X/R:X/V:X/RE:X/U:X
Am I affected? How to checkSteps we derive from the advisory and the affected-version data, so you can decide whether this CVE reaches your setup. They are a guide, not a scan — your own configuration is the authority.
dbcve checksWork through these to decide whether this CVE applies to you.
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Identify Protobuf PHP library installationLocate the Protobuf PHP library in your project by searching for 'protobuf' in composer.json or by checking for the presence of the vendor/google/protobuf-php directoryAffected if The Protobuf PHP library is present in the environment
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Determine installed Protobuf PHP versionRun 'composer show google/protobuf-php' or check the version field in vendor/google/protobuf-php/composer.jsonAffected if The installed version is lower than the patched version (compare to the latest release once available)
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Check if application parses untrusted protobuf messagesSearch codebase for calls to methods like 'parse', 'parseFromString', or 'mergeFromString' that process externally-supplied protobuf dataAffected if The application parses protobuf messages from untrusted sources (user input, API requests, external services)
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Identify if negative varint or recursive message parsing is possibleReview the structure of expected protobuf message definitions (.proto files) for fields that could contain negative integers or deeply nested message structuresAffected if Protobuf schemas allow negative varint values or deep message nesting that could trigger the vulnerability
The environment is affected if the Protobuf PHP library is installed and parses untrusted protobuf messages containing negative varints or deeply nested structures.
Generated from the published advisory. Verify against your own configuration.
Remediation Closing itWhat it takes to close this. Where a vendor fix exists we point at it; where none exists we say so plainly, and can build one. Effort estimates are scoped from the advisory, not from your codebase.
From vendor dataUpdate the Protobuf PHP library to the latest patched version once released. In the interim, implement input validation before passing untrusted data to the protobuf parser and consider deploying the service behind load balancers with health checks for resilience.
- Consultation3.0 h
- Implementation6.0 h
- Testing4.0 h
- Review / QA2.0 h
An estimate, not a bill — we confirm scope with you before any work starts. Need it this week? Rush from $4,224.
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Free · runs locallyCheck whether your project pulls in CVE-2026-6409 — or any other known-vulnerable package — straight from your lock files. Free and open source; it runs locally and uploads nothing.
References Go to the primary sourcePrimary sources — vendor advisories, patches and trackers. Where our summary and a reference disagree, the reference wins.
Primary sourcesPractitioner notes
ContributedPeer-ranked notes from engineers who’ve handled CVE-2026-6409 in production — separate from our analysis above.
The advisory tells you what broke. It rarely tells you what actually worked. If you’ve dealt with this one, that detail is what the next engineer is searching for.
- The version that genuinely resolved it — not the one the vendor claimed
- A config change or rule that shut the vector down
- A gotcha in the upgrade path that cost you an afternoon
No notes yet
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- Verified mitigations, workarounds, and config changes
- Version or environment caveats, and links to real fixes
- No weaponised exploit code, or anything meant to cause harm
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