CVE-2026-39984: Github.com/sigstore/timestamp authority/v2 Improper Certificate Validation Vulnerability
MODERATECVE-2026-39984 is a MODERATE (CVSS 5.5) improper certificate validation vulnerability (CWE-295: Improper Certificate Validation) affecting Github.com/sigstore/timestamp authority/v2 libraries in the Go ecosystem. The issue involves sigstore timestamp authority has improper certificate validation in verifier. Remediation is available by upgrading affected packages to version 2.0.6.
CVE-2026-39984 at a Glance
Security Impact
CVSS: 5.5
The security impact metrics below are parsed directly from the CVSS v3.1 vector string (CVSS:3.1/AV:L/AC:L/PR:N/UI:R/S:U/C:N/I:H/A:N).
How to Fix CVE-2026-39984
To remediate this vulnerability, upgrade all affected Github.com/sigstore/timestamp authority/v2 dependencies to a patched release. Both direct and transitive dependencies should be checked, as frameworks or security libraries may pull in vulnerable versions transitively.
Upgrade github.com/sigstore/timestamp-authority/v2 to 2.0.6Run the following command in your project directory to verify that all resolved dependencies use the patched release:
inspect dependencies for github.com/sigstore/timestamp-authority/v2How to Check if You Are Affected
To determine whether your application is affected by CVE-2026-39984, inspect your project dependencies for Github.com/sigstore/timestamp authority/v2:
inspect dependencies for github.com/sigstore/timestamp-authority/v2Analyze the terminal output to locate any version of Github.com/sigstore/timestamp authority/v2 in your dependency tree. If any resolved version matches the vulnerable ranges listed in the table below (for example, versions earlier than 2.0.6), your application is affected.
Note: Verify declared build manifests and deployed runtime container environments.
Technical Details
Vulnerability Mechanism & Technical Analysis
This vulnerability is classified under CWE-295: Improper Certificate Validation, where the product does not validate, or incorrectly validates, a certificate. In Github.com/sigstore/timestamp authority/v2, software state validation or input boundaries are circumvented during processing. Review the official source advisory statement below for specific affected components, classes, and reproduction details.
Source Advisory Statement
CVE-2026-39984 Affected Github.com/sigstore/timestamp authority/v2 Versions
1 component(s)| Product / Package | Ecosystem | Affected Versions | Fixed Version |
|---|---|---|---|
|
github.com/sigstore/timestamp-authority/v2
|
Go |
< 2.0.6
|
2.0.6
|
References
Frequently Asked Questions
What is CVE-2026-39984?
Which Github.com/sigstore/timestamp authority/v2 versions are affected?
What version fixes CVE-2026-39984?
Is github.com/sigstore/timestamp-authority/v2 affected?
What is the CVSS score of CVE-2026-39984?
What CWE is associated with CVE-2026-39984?
How can I check Go dependencies for CVE-2026-39984?
Machine-readable OSV JSON
OSV v1.5 Schema
{
"schema_version" : "1.4.0",
"id" : "GHSA-xm5m-wgh2-rrg3",
"modified" : "2026-04-24T20:43:09Z",
"published" : "2026-04-14T01:01:59Z",
"aliases" : [ "CVE-2026-39984" ],
"summary" : "Sigstore Timestamp Authority has Improper Certificate Validation in verifier",
"details" : "### Authorization bypass via certificate bag manipulation in sigstore/timestamp-authority verifier\n\nAn 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. \n\nThis vulnerability does **not** apply to timestamp-authority service, only to users of `timestamp-authority/v2/pkg/verification` package.\n\nThis 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.\n\n\n### Patches\n\nThe issue will be fixed in timestamp-authority 2.0.6\n\n### Workarounds\n\nUsers of `VerifyTimestampResponse` can use the `TSACertificate` option to specify the exact certificate they expect to be used: this fully mitigates the issue.\n\n### References\n\nThis issue was found after reading CVE-2026-33753 / GHSA-3xxc-pwj6-jgrj (originally reported by @Jaynornj and @Pr00fOf3xpl0it)",
"severity" : [ {
"type" : "CVSS_V3",
"score" : "CVSS:3.1/AV:L/AC:L/PR:N/UI:R/S:U/C:N/I:H/A:N"
} ],
"affected" : [ {
"package" : {
"ecosystem" : "Go",
"name" : "github.com/sigstore/timestamp-authority/v2"
},
"ranges" : [ {
"type" : "ECOSYSTEM",
"events" : [ {
"introduced" : "0"
}, {
"fixed" : "2.0.6"
} ]
} ],
"database_specific" : {
"last_known_affected_version_range" : "<= 2.0.5"
}
} ],
"references" : [ {
"type" : "WEB",
"url" : "https://github.com/sigstore/timestamp-authority/security/advisories/GHSA-xm5m-wgh2-rrg3"
}, {
"type" : "ADVISORY",
"url" : "https://nvd.nist.gov/vuln/detail/CVE-2026-39984"
}, {
"type" : "PACKAGE",
"url" : "https://github.com/sigstore/timestamp-authority"
}, {
"type" : "WEB",
"url" : "https://github.com/sigstore/timestamp-authority/releases/tag/v2.0.6"
} ],
"database_specific" : {
"cwe_ids" : [ "CWE-295" ],
"severity" : "MODERATE",
"github_reviewed" : true,
"github_reviewed_at" : "2026-04-14T01:01:59Z",
"nvd_published_at" : "2026-04-15T04:17:40Z"
}
}