CVE-2026-39395: Github.com/sigstore/cosign Cosign's Verify-blob-attestation Reports False Positive Vulnerability
MODERATECVE-2026-39395 is a MODERATE (CVSS 4.3) cosign's verify-blob-attestation reports false positive vulnerability (CWE-754: Improper Check for Unusual or Exceptional Conditions) affecting Github.com/sigstore/cosign libraries in the Go ecosystem. The issue involves cosign's verify-blob-attestation reports false positive when payload parsing fails. Remediation is available by upgrading affected packages to version 3.0.6, 2.6.3.
CVE-2026-39395 at a Glance
Security Impact
CVSS: 4.3
The security impact metrics below are parsed directly from the CVSS v3.1 vector string (CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:N/I:L/A:N).
How to Fix CVE-2026-39395
To remediate this vulnerability, upgrade all affected Github.com/sigstore/cosign 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/cosign to 3.0.6Upgrade github.com/sigstore/cosign to 2.6.3Run the following command in your project directory to verify that all resolved dependencies use the patched release:
inspect dependencies for github.com/sigstore/cosignHow to Check if You Are Affected
To determine whether your application is affected by CVE-2026-39395, inspect your project dependencies for Github.com/sigstore/cosign:
inspect dependencies for github.com/sigstore/cosignAnalyze the terminal output to locate any version of Github.com/sigstore/cosign in your dependency tree. If any resolved version matches the vulnerable ranges listed in the table below (for example, versions earlier than 3.0.6), 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-754: Improper Check for Unusual or Exceptional Conditions, where the product does not check or incorrectly checks for unusual or exceptional conditions that are not expected to occur frequently during day to day operation of the product. In Github.com/sigstore/cosign, 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-2026-39395 Affected Github.com/sigstore/cosign Versions
2 component(s)| Product / Package | Ecosystem | Affected Versions | Fixed Version |
|---|---|---|---|
|
github.com/sigstore/cosign
|
Go |
≥ 3.0.0
< 3.0.6
|
3.0.6
|
|
github.com/sigstore/cosign
|
Go |
< 2.6.3
|
2.6.3
|
References
Frequently Asked Questions
What is CVE-2026-39395?
Which Github.com/sigstore/cosign versions are affected?
What version fixes CVE-2026-39395?
Is github.com/sigstore/cosign affected?
What is the CVSS score of CVE-2026-39395?
What CWE is associated with CVE-2026-39395?
How can I check Go dependencies for CVE-2026-39395?
Machine-readable OSV JSON
OSV v1.5 Schema
{
"schema_version" : "1.4.0",
"id" : "GHSA-w6c6-c85g-mmv6",
"modified" : "2026-04-08T00:15:44Z",
"published" : "2026-04-08T00:15:44Z",
"aliases" : [ "CVE-2026-39395" ],
"summary" : "Cosign's verify-blob-attestation reports false positive when payload parsing fails",
"details" : "## Description\n\n`cosign verify-blob-attestation` may erroneously report a \"Verified OK\" result for attestations with malformed payloads or mismatched predicate types. For old-format bundles and detached signatures, this was due to a logic flaw in the error handling of the predicate type validation. For new-format bundles, the predicate type validation was bypassed completely.\n\n## Impact\n\nWhen `cosign verify-blob-attestation` is used without `--check-claims` set to `true`, an attestation that has a valid signature but a malformed or unparsable payload would be incorrectly validated. Additionally, systems relying on `--type <predicate type>` to reject attestations with mismatched types would be lead to trust the unexpected attestation type.\n\n## Patches\n\nv3.0.6, v2.6.3\n\n## Workarounds\n\nAlways set `--check-claims=true` for attestation verification.",
"severity" : [ {
"type" : "CVSS_V3",
"score" : "CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:N/I:L/A:N"
} ],
"affected" : [ {
"package" : {
"ecosystem" : "Go",
"name" : "github.com/sigstore/cosign"
},
"ranges" : [ {
"type" : "ECOSYSTEM",
"events" : [ {
"introduced" : "3.0.0"
}, {
"fixed" : "3.0.6"
} ]
} ]
}, {
"package" : {
"ecosystem" : "Go",
"name" : "github.com/sigstore/cosign"
},
"ranges" : [ {
"type" : "ECOSYSTEM",
"events" : [ {
"introduced" : "0"
}, {
"fixed" : "2.6.3"
} ]
} ]
} ],
"references" : [ {
"type" : "WEB",
"url" : "https://github.com/sigstore/cosign/security/advisories/GHSA-w6c6-c85g-mmv6"
}, {
"type" : "ADVISORY",
"url" : "https://nvd.nist.gov/vuln/detail/CVE-2026-39395"
}, {
"type" : "PACKAGE",
"url" : "https://github.com/sigstore/cosign"
} ],
"database_specific" : {
"cwe_ids" : [ "CWE-754" ],
"severity" : "MODERATE",
"github_reviewed" : true,
"github_reviewed_at" : "2026-04-08T00:15:44Z",
"nvd_published_at" : "2026-04-07T20:16:33Z"
}
}