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CVE-2026-39984— Sigstore Timestamp Authority has Improper Certificate Validation in verifier

Quick assessment

Affected
sigstore timestamp-authority
Exploitation
No confirmed in-the-wild exploitation; assess based on exposure
Recommended action
Check the vendor advisory and references for a fixed version. If immediate upgrade is impossible, restrict exposure and increase monitoring.

Sigstore Timestamp Authority是sigstore开源的一个RFC3161时间戳授权软件。 Sigstore Timestamp Authority 2.0.5及之前版本存在安全漏洞，该漏洞源于VerifyTimestampResponse函数存在授权绕过问题，可能导致验证签名与授权检查不一致。

CVSS 5.5 · Medium EPSS 0.11% · P1

Possible ATT&CK Techniques 1 AI

T1190 · Exploit Public-Facing Application
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I. Basic Information for CVE-2026-39984

Vulnerability Information
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Vulnerability Title
Sigstore Timestamp Authority has Improper Certificate Validation in verifier
Source: CVE Program / CVE List V5
Vulnerability 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.
Source: CVE Program / CVE List V5
CVSS Information
CVSS:3.1/AV:L/AC:L/PR:N/UI:R/S:U/C:N/I:H/A:N
Source: CVE Program / CVE List V5
Vulnerability Type
证书验证不恰当
Source: CVE Program / CVE List V5
Vulnerability Title
Sigstore Timestamp Authority 安全漏洞
Source: CNNVD (China National Vulnerability Database)
Vulnerability Description
Sigstore Timestamp Authority是sigstore开源的一个RFC3161时间戳授权软件。 Sigstore Timestamp Authority 2.0.5及之前版本存在安全漏洞，该漏洞源于VerifyTimestampResponse函数存在授权绕过问题，可能导致验证签名与授权检查不一致。
Source: CNNVD (China National Vulnerability Database)
CVSS Information
N/A
Source: CNNVD (China National Vulnerability Database)
Vulnerability Type
N/A
Source: CNNVD (China National Vulnerability Database)

Affected Products

Vendor Product Affected Versions CPE Subscribe
sigstore timestamp-authority < 2.0.6 -

II. Public POCs for CVE-2026-39984

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III. Intelligence Information for CVE-2026-39984

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Vendor Advisories for CVE-2026-39984 (1)

IV. Related Vulnerabilities

Same product: timestamp-authority
Same vendor: sigstore
Same weakness: CWE-295

V. Comments for CVE-2026-39984

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