dbcve.org
Sigstore Timestamp AuthorityApplication · Linuxfoundation

CVE-2026-39984

MEDIUM · 5.5 CVSS v3.1 Published 2026-04-15
Fix available
A fix is available. Upgrade to 2.0.6 or later.
See remediation →
58/100
Remediation priority · Elevated
No privileges

Official description Straight from the sourceThe vendor's or NVD's own wording, published unedited. Authoritative, but often terse — it says what broke, rarely what to do.

NVD · unedited
Sigstore Timestamp Authority is a service for issuing RFC 3161 timestamps. Versions 2.0.5 and below contain an authorization bypass vulnerability in the VerifyTimestampResponse function. VerifyTimestampResponse correctly verifies the certificate chain signature, but the TSA-specific constraint checks in VerifyLeafCert uses the first non-CA certificate from the PKCS#7 certificate bag instead of the leaf certificate from the verified chain. An attacker can exploit this by prepending a forged certificate to the certificate bag while the message is signed with an authorized key, causing the library to validate the signature against one certificate but perform authorization checks against another. This vulnerability only affects users of the timestamp-authority/v2/pkg/verification package and does not affect the timestamp-authority service itself or sigstore-go. The issue has been fixed in version 2.0.6.

Technical summary Written by usOur analysis, written from the advisory, the CVSS vector and the affected-version data. It adds context the advisory leaves out, and never invents facts that are not in the source.

dbcve analysis · high confidence

The VerifyTimestampResponse function in Sigstore Timestamp Authority's verification package has an authorization bypass where TSA-specific constraint checks use the first non-CA certificate from the PKCS#7 certificate bag instead of the leaf certificate from the verified chain. An attacker can prepend a forged certificate to the certificate bag, causing the library to validate the signature against one certificate (the legitimate signing key) but perform authorization checks against another (the forged certificate).

MitigationUsers of the timestamp-authority/v2/pkg/verification package should upgrade to version 2.0.6 or later. The timestamp-authority service and sigstore-go are not affected.

Verify against the referenced sources before acting — the references below are authoritative for this CVE, this summary is not.

Affected products & versions What the vendor confirmedThe version ranges the vendor confirmed as vulnerable. If your version sits inside a range here, treat yourself as exposed until you have upgraded.

NVD · CPE data
Sigstore Timestamp AuthorityApplication
Affected:< 2.0.6

CVSS breakdown How the score is builtThe industry scoring standard. It rates how the flaw is reached, what it takes to exploit, and what an attacker gains — the score is derived from those, not the other way round.

From the vector
Attack vector
Local
Complexity
Low
Privileges
None
User interaction
Required
Scope
Unchanged
Confidentiality
None
Integrity
High
Availability
None

CVSS:3.1/AV:L/AC:L/PR:N/UI:R/S:U/C:N/I:H/A:N

Am I affected? How to checkSteps we derive from the advisory and the affected-version data, so you can decide whether this CVE reaches your setup. They are a guide, not a scan — your own configuration is the authority.

dbcve checks

Work through these to decide whether this CVE applies to you.

  1. Check the installed version of timestamp-authority verification package
    Run 'go list -m all | grep timestamp-authority' or inspect your go.mod file for 'timestamp-authority/v2/pkg/verification' and note the version number
    Affected if The version listed is less than 2.0.6 (for example, 2.0.5, 2.0.4, etc.)
  2. Verify the verification package is in use
    Search your codebase for imports of 'timestamp-authority/v2/pkg/verification' using grep or your IDE's search functionality
    Affected if The package 'timestamp-authority/v2/pkg/verification' is imported and used in your project
  3. Confirm VerifyTimestampResponse function is called
    Search your codebase for calls to 'VerifyTimestampResponse' function, which is the vulnerable function in the verification package
    Affected if Your code directly invokes VerifyTimestampResponse for timestamp verification

You are affected if you are using timestamp-authority/v2/pkg/verification version lower than 2.0.6 and your code performs timestamp verification via the VerifyTimestampResponse function.

Generated from the published advisory. Verify against your own configuration.

Check your environment

Paste your version and any relevant configuration and it will be compared against the affected criteria above. Do not include secrets or credentials.

AI-assisted, checked against the advisory. Informational, not a guarantee.

Remediation Closing itWhat it takes to close this. Where a vendor fix exists we point at it; where none exists we say so plainly, and can build one. Effort estimates are scoped from the advisory, not from your codebase.

dbcve · scoped
Upgrade available Upgrade to 2.0.6 or later
Fixed in 2.0.6
Interim mitigation

Users of the timestamp-authority/v2/pkg/verification package should upgrade to version 2.0.6 or later. The timestamp-authority service and sigstore-go are not affected.

Recommended fix High confidence

Sigstore Timestamp Authority version 2.0.6

  1. 1. Identify all code that imports and uses the timestamp-authority/v2/pkg/verification package
  2. 2. Update the dependency to version 2.0.6 or later (e.g., go get github.com/sigstore/[email protected] or latest)
  3. 3. Rebuild and test the affected applications
  4. 4. Redeploy the updated applications

Generated from the published advisory — verify against the referenced sources before acting.

Fix this in Sigstore Timestamp Authority Scoped from the published advisory
  • Consultation1.0 h
  • Implementation2.0 h
  • Testing2.0 h
  • Review / QA1.0 h
6.0 hours of engineering $1,040
Get the upgrade done

An estimate, not a bill — we confirm scope with you before any work starts. Need it this week? Rush from $1,664.

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References Go to the primary sourcePrimary sources — vendor advisories, patches and trackers. Where our summary and a reference disagree, the reference wins.

Primary sources

Practitioner notes

Contributed

Peer-ranked notes from engineers who’ve handled CVE-2026-39984 in production — separate from our analysis above.

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What this is

A place for practitioners to share what actually worked: a mitigation you’ve tested, a configuration change, a version- or environment-specific caveat, or a link to a verified patch. The most useful notes rise to the top as peers upvote them, so the signal stays high.

What belongs here
  • Verified mitigations, workarounds, and config changes
  • Version or environment caveats, and links to real fixes
  • No weaponised exploit code, or anything meant to cause harm
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