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sigstore-go has a multi-log threshold bypass via single compromised log

Moderate severity GitHub Reviewed Published Jun 4, 2026 in sigstore/sigstore-go • Updated Jul 31, 2026

Package

gomod github.com/sigstore/sigstore-go (Go)

Affected versions

<= 1.1.4

Patched versions

1.2.0

Description

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.

References

@Hayden-IO Hayden-IO published to sigstore/sigstore-go Jun 4, 2026
Published to the GitHub Advisory Database Jul 9, 2026
Reviewed Jul 9, 2026
Published by the National Vulnerability Database Jul 17, 2026
Last updated Jul 31, 2026

Severity

Moderate

CVSS overall score

This score calculates overall vulnerability severity from 0 to 10 and is based on the Common Vulnerability Scoring System (CVSS).
/ 10

CVSS v3 base metrics

Attack vector
Network
Attack complexity
High
Privileges required
None
User interaction
None
Scope
Unchanged
Confidentiality
None
Integrity
High
Availability
None

CVSS v3 base metrics

Attack vector: More severe the more the remote (logically and physically) an attacker can be in order to exploit the vulnerability.
Attack complexity: More severe for the least complex attacks.
Privileges required: More severe if no privileges are required.
User interaction: More severe when no user interaction is required.
Scope: More severe when a scope change occurs, e.g. one vulnerable component impacts resources in components beyond its security scope.
Confidentiality: More severe when loss of data confidentiality is highest, measuring the level of data access available to an unauthorized user.
Integrity: More severe when loss of data integrity is the highest, measuring the consequence of data modification possible by an unauthorized user.
Availability: More severe when the loss of impacted component availability is highest.
CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:N/I:H/A:N

EPSS score

Exploit Prediction Scoring System (EPSS)

This score estimates the probability of this vulnerability being exploited within the next 30 days. Data provided by FIRST.
(7th percentile)

Weaknesses

Insufficient Verification of Data Authenticity

The product does not sufficiently verify the origin or authenticity of data, in a way that causes it to accept invalid data. Learn more on MITRE.

Improper Verification of Cryptographic Signature

The product does not verify, or incorrectly verifies, the cryptographic signature for data. Learn more on MITRE.

CVE ID

CVE-2026-49834

GHSA ID

GHSA-9vcr-p3rj-q5q6

Source code

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