sigstore-go has a multi-log threshold bypass via single compromised log in github.com/sigstore/sigstore-go

Open Source Vulnerabilities CVE-2026-49834

sigstore-go is a Go library for Sigstore signing and verification. Prior to 1.2.0, a verifier configured with WithTransparencyLog(N>1) or WithSignedCertificateTimestamps(N>1) counts verified witnesses per entry or per validation path rather than per log authority, allowing a single compromised transparency log or CT log to satisfy multi-log threshold requirements and defeat the multi-log policy. This issue is fixed in version 1.2.0.

Open Source Vulnerabilities GO-2026-5952

sigstore-go has a multi-log threshold bypass via single compromised log in github.com/sigstore/sigstore-go

Open Source Vulnerabilities GHSA-9vcr-p3rj-q5q6

### Impact _What kind of vulnerability is it? Who is impacted?_ A verifier configured with WithTransparencyLog(N>1) or WithSignedCertificateTimestamps(N>1) expected defense-in-depth against the compromise of a single log instance. However, threshold counting counted verified witnesses per-entry or per-validation-path rather than per-log-authority. As a result, a single compromised transparency log could forge multiple entries with different indices, and a single compromised CT log could verify multiple times (either across multiple certificate chains or via multiple embedded SCTs), fully satisfying the multi-log threshold requirements and defeating the multi-log policy. Note that this does not affect Cosign, as Cosign sets a threshold of 1. ### Patches _Has the problem been patched? What versions should users upgrade to?_ Upgrade to v1.1.5. ### Workarounds _Is there a way for users to fix or remediate the vulnerability without upgrading?_ There is no workaround, beyond relying on trusted logs.