How severe is CVE-2026-6409?

CVE-2026-6409 has a CVSS 4.0 base score of 7.1, rated high severity.

Is CVE-2026-6409 being actively exploited?

It is not currently listed in CISA's KEV catalog. Its EPSS exploit-prediction score is 0% (28th percentile), an estimate of the probability of exploitation in the next 30 days.

How do I fix CVE-2026-6409?

Review the linked vendor and NVD advisories for patched versions and mitigations, then upgrade or apply the recommended workaround. Given its high severity, prioritise patching exposed systems.

Does CVE-2026-6409 have an EU (EUVD) identifier?

Yes. CVE-2026-6409 is tracked in the ENISA EU Vulnerability Database (EUVD) as EUVD-2026-23268.

When was CVE-2026-6409 published?

CVE-2026-6409 was published on 2026-04-16 and last updated on 2026-06-17.

CVE-2026-6409

CVE-2026-6409 is a high-severity vulnerability with a CVSS 4.0 base score of 7.1. It is not currently listed as actively exploited by CISA, and its EPSS exploit-prediction score is low. The underlying weakness is classified as CWE-20.

Key facts

Severity: High (CVSS 4.0 base score 7.1)
EPSS exploit prediction: 0% (28th percentile)
Actively exploited: Not listed in CISA KEV
EU (EUVD) id: EUVD-2026-23268
Weakness: CWE-20
Published: 2026-04-16
Last modified: 2026-06-17

Description

A 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.

Frequently asked questions

What is CVE-2026-6409?: A 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.
How severe is CVE-2026-6409?: CVE-2026-6409 has a CVSS 4.0 base score of 7.1, rated high severity.
Is CVE-2026-6409 being actively exploited?: It is not currently listed in CISA's KEV catalog. Its EPSS exploit-prediction score is 0% (28th percentile), an estimate of the probability of exploitation in the next 30 days.
How do I fix CVE-2026-6409?: Review the linked vendor and NVD advisories for patched versions and mitigations, then upgrade or apply the recommended workaround. Given its high severity, prioritise patching exposed systems.
Does CVE-2026-6409 have an EU (EUVD) identifier?: Yes. CVE-2026-6409 is tracked in the ENISA EU Vulnerability Database (EUVD) as EUVD-2026-23268.
When was CVE-2026-6409 published?: CVE-2026-6409 was published on 2026-04-16 and last updated on 2026-06-17.

References

https://github.com/protocolbuffers/protobuf/security/advisories/GHSA-p2gh-cfq4-4wjc

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