How severe is CVE-2026-39984?

CVE-2026-39984 has a CVSS 3.x base score of 5.5, rated medium severity. It is exploitable over local access with low attack complexity, requires no privileges and user interaction. Impact on confidentiality is none, integrity high, and availability none.

Is CVE-2026-39984 being actively exploited?

It is not currently listed in CISA's KEV catalog. Its EPSS exploit-prediction score is 0% (1st percentile), an estimate of the probability of exploitation in the next 30 days.

What products are affected by CVE-2026-39984?

CVE-2026-39984 affects Linuxfoundation Sigstore Timestamp Authority. See the affected-products list for the exact vulnerable versions.

How do I fix CVE-2026-39984?

Review the linked vendor and NVD advisories for patched versions and mitigations, then upgrade or apply the recommended workaround.

Does CVE-2026-39984 have an EU (EUVD) identifier?

Yes. CVE-2026-39984 is tracked in the ENISA EU Vulnerability Database (EUVD) as EUVD-2026-22813.

When was CVE-2026-39984 published?

CVE-2026-39984 was published on 2026-04-15 and last updated on 2026-06-17.

CVE-2026-39984

CVE-2026-39984 is a medium-severity vulnerability in Linuxfoundation Sigstore Timestamp Authority with a CVSS 3.x base score of 5.5. It is not currently listed as actively exploited by CISA, and its EPSS exploit-prediction score is low. The underlying weakness is classified as CWE-295.

Key facts

Severity: Medium (CVSS 3.x base score 5.5)
EPSS exploit prediction: 0% (1st percentile)
Actively exploited: Not listed in CISA KEV
EU (EUVD) id: EUVD-2026-22813
Weakness: CWE-295
Affected product: Linuxfoundation Sigstore Timestamp Authority
Published: 2026-04-15
Last modified: 2026-06-17

Description

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.

Frequently asked questions

What is CVE-2026-39984?: 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.
How severe is CVE-2026-39984?: CVE-2026-39984 has a CVSS 3.x base score of 5.5, rated medium severity. It is exploitable over local access with low attack complexity, requires no privileges and user interaction. Impact on confidentiality is none, integrity high, and availability none.
Is CVE-2026-39984 being actively exploited?: It is not currently listed in CISA's KEV catalog. Its EPSS exploit-prediction score is 0% (1st percentile), an estimate of the probability of exploitation in the next 30 days.
What products are affected by CVE-2026-39984?: CVE-2026-39984 affects Linuxfoundation Sigstore Timestamp Authority. See the affected-products list for the exact vulnerable versions.
How do I fix CVE-2026-39984?: Review the linked vendor and NVD advisories for patched versions and mitigations, then upgrade or apply the recommended workaround.
Does CVE-2026-39984 have an EU (EUVD) identifier?: Yes. CVE-2026-39984 is tracked in the ENISA EU Vulnerability Database (EUVD) as EUVD-2026-22813.
When was CVE-2026-39984 published?: CVE-2026-39984 was published on 2026-04-15 and last updated on 2026-06-17.

References

Affected products (1)

cpe:2.3:a:linuxfoundation:sigstore_timestamp_authority:*:*:*:*:*:*:*:*

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