Bug 2456254 (CVE-2026-39395)

Summary: CVE-2026-39395 github.com/sigstore/cosign: Cosign: Incorrect attestation verification due to malformed payloads or mismatched predicate types
Product: [Other] Security Response Reporter: OSIDB Bzimport <bzimport>
Component: vulnerabilityAssignee: Product Security DevOps Team <prodsec-dev>
Status: NEW --- QA Contact:
Severity: medium Docs Contact:
Priority: medium    
Version: unspecifiedCC: agarcial, akoudelk, aoconnor, asegurap, dhanak, drosa, dsimansk, eborisov, jburrell, kingland, kverlaen, lball, lbragsta, mnovotny, ngough, sausingh, veshanka, wenshen
Target Milestone: ---Keywords: Security
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Hardware: All   
OS: Linux   
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A flaw was found in Cosign, a tool for code signing and transparency for containers and binaries. A remote attacker could exploit this vulnerability by providing malformed payloads or attestations with mismatched predicate types. This could lead to Cosign erroneously reporting a "Verified OK" result, even when the attestations are invalid. This issue compromises the integrity of the verification process, potentially allowing unverified software to be trusted.
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oVirt Team: --- RHEL 7.3 requirements from Atomic Host:
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Bug Depends On: 2456380, 2456377, 2456378, 2456379    
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Description OSIDB Bzimport 2026-04-07 21:01:55 UTC
Cosign provides code signing and transparency for containers and binaries. Prior to 3.0.6 and 2.6.3, cosign verify-blob-attestation may erroneously report a "Verified OK" result for attestations with malformed payloads or mismatched predicate types. For old-format bundles and detached signatures, this was due to a logic flaw in the error handling of the predicate type validation. For new-format bundles, the predicate type validation was bypassed completely. This vulnerability is fixed in 3.0.6 and 2.6.3.