CVE-2026-39984

mediumpriority · track · 0EPSS 0.001 · 1 %ileDEEUFRUS
grimoire priorityP3 · Track
Exploitable?
—
no known exploitation
Likely / severe?
0.10% (1st) EPSS
CVSS 5.5 · medium
Is it mine?
6 products
Check your exposure
Who says so?
6 sources
cnnvd · enisa_euvd · osv · cert_bund

EPSS · scored 2026-10-27

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.

01

cvss

Technical severity, 0–10. One row per scoring source.

5.5
010

base score 0–10 · higher = more severe · hover a vector to decode

v3.15.5mediumCVSS:3.1/AV:L/AC:L/PR:N/UI:R/S:U/C:N/I:H/A:Nsecondary · ENISA EU
v3.15.5mediumCVSS:3.1/AV:L/AC:L/PR:N/UI:R/S:U/C:N/I:H/A:Nsecondary · security-advisories@github.comexploitability 1.8 · impact 3.6
v3.15.5mediumCVSS:3.1/AV:L/AC:L/PR:N/UI:R/S:U/C:N/I:H/A:Nsecondary · OSV
v3.15.1mediumCVSS:3.1/AV:L/AC:L/PR:N/UI:R/S:U/C:N/I:H/A:N/E:Usecondary · CVSS-BT (t0sche)
02

ssvc

A stakeholder decision — act, attend, or track — from exploitation and impact.

Trackcoordinatorcisa_ssvcUS
03

weaknesses

The CWE weakness classes this flaw belongs to.

CWE-295USCWE-295US
04

affected products (6)

Products and version ranges known to be affected.

05

advisories (4)

Vendor and ecosystem advisories describing this.

  • WID-SEC-W-2026-3046IBM Concert: Mehrere SchwachstellenDeutsch2026-08-26csaf · cert_bundDE

    Ein Angreifer kann mehrere Schwachstellen in IBM Concert ausnutzen, um beliebigen Programmcode auszuführen, um einen Denial of Service Angriff durchzuführen, um Informationen offenzulegen, um Dateien zu manipulieren, um einen Cross-Site Scripting Angriff durchzuführen, um einen SQL-Injection Angriff durchzuführen und um Sicherheitsvorkehrungen zu umgehen.

  • GHSA-xm5m-wgh2-rrg3Sigstore Timestamp Authority has Improper Certificate Validation in verifier2026-04-14ghsa · osvUS

    ### Authorization bypass via certificate bag manipulation in sigstore/timestamp-authority verifier An authorization bypass vulnerability exists in sigstore/timestamp-authority verifier (timestamp-authority/v2/pkg/verification): `VerifyTimestampResponse` function correctly verifies the certificate chain but when the TSA specific constraints are verified in `VerifyLeafCert`, the first non-CA certificate from the PKCS#7 certificate bag is used instead of the leaf certificate from the certificate chain. An attacker can exploit this by prepending a forged certificate to the certificate bag while the message is signed with an authorized key. The library validates the signature using the one certificate but performs authorization checks on the another, allowing an attacker to bypass some authorization controls. This vulnerability does **not** apply to timestamp-authority service, only to users of `timestamp-authority/v2/pkg/verification` package. This vulnerability does **not** apply to sigstore-go even though it is a user of `timestamp-authority/v2/pkg/verification`: Providing `TSACertificate` option to `VerifyTimestampResponse` fully mitigates the issue. ### Patches The issue will be fixed in timestamp-authority 2.0.6 ### Workarounds Users of `VerifyTimestampResponse` can use the `TSACertificate` option to specify the exact certificate they expect to be used: this fully mitigates the issue. ### References This issue was found after reading CVE-2026-33753 / GHSA-3xxc-pwj6-jgrj (originally reported by @Jaynornj and @Pr00fOf3xpl0it)

  • CERTFR-2026-AVI-1385Multiples vulnérabilités dans les produits VMwareFrançais2026-10-26vendor · certfrFR
  • GO-2026-5763Sigstore Timestamp Authority has Improper Certificate Validation in verifier in github.com/sigstore/timestamp-authority2026-06-25vendor · osvUS

    Sigstore Timestamp Authority has Improper Certificate Validation in verifier in github.com/sigstore/timestamp-authority

06

also known as (5)

Other names and identifiers for this entity.

07

sources

Which sources assert this record, and when.

cnnvdenisa_euvdosvcert_bundnvdcertfrNVDCVE.orgMITRE
published 2026-04-15modified 2026-10-26
08

references (6)

External citations — patches, advisories, analysis.

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