CVE-2026-49834: sigstore-go: Multi-log threshold bypass via single compromised log
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.
Other sources
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.
— MITRE
Affected Software
Remediation
Recommended actions to resolve this vulnerability, in priority order.
- Upgrade
Upgrade
go/github.com/sigstore/sigstore-goto a version that resolves this vulnerability.Fixed in 1.2.0 - Upgrade
Upgrade
sigstore-goto a version that resolves this vulnerability.Fixed in 1.2.0
Event History
Frequently Asked Questions
What is the severity of CVE-2026-49834?
The severity of CVE-2026-49834 is categorized as medium with a score of 5.9.
Who is impacted by CVE-2026-49834?
CVE-2026-49834 impacts verifiers configured with multiple transparency logs or signed certificate timestamps.
How do I fix CVE-2026-49834?
To fix CVE-2026-49834, ensure that your verifier is not relying on a single log instance and review the configuration for transparency logging.
What type of vulnerability is CVE-2026-49834?
CVE-2026-49834 is a vulnerability related to the verification process of logs in systems using transparency logs.
What is the impact of CVE-2026-49834 on data integrity?
CVE-2026-49834 poses a risk to data integrity as it allows the potential compromise of verified logs, leading to unauthorized actions.