GHSA-W6C6-C85G-MMV6
Vulnerability from github – Published: 2026-04-08 00:15 – Updated: 2026-04-08 00:15
VLAI?
Summary
Cosign's verify-blob-attestation reports false positive when payload parsing fails
Details
Description
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.
Impact
When 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.
Patches
v3.0.6, v2.6.3
Workarounds
Always set --check-claims=true for attestation verification.
Severity ?
4.3 (Medium)
{
"affected": [
{
"package": {
"ecosystem": "Go",
"name": "github.com/sigstore/cosign"
},
"ranges": [
{
"events": [
{
"introduced": "3.0.0"
},
{
"fixed": "3.0.6"
}
],
"type": "ECOSYSTEM"
}
]
},
{
"package": {
"ecosystem": "Go",
"name": "github.com/sigstore/cosign"
},
"ranges": [
{
"events": [
{
"introduced": "0"
},
{
"fixed": "2.6.3"
}
],
"type": "ECOSYSTEM"
}
]
}
],
"aliases": [
"CVE-2026-39395"
],
"database_specific": {
"cwe_ids": [
"CWE-754"
],
"github_reviewed": true,
"github_reviewed_at": "2026-04-08T00:15:44Z",
"nvd_published_at": "2026-04-07T20:16:33Z",
"severity": "MODERATE"
},
"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 \u003cpredicate type\u003e` 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.",
"id": "GHSA-w6c6-c85g-mmv6",
"modified": "2026-04-08T00:15:44Z",
"published": "2026-04-08T00:15:44Z",
"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"
}
],
"schema_version": "1.4.0",
"severity": [
{
"score": "CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:N/I:L/A:N",
"type": "CVSS_V3"
}
],
"summary": "Cosign\u0027s verify-blob-attestation reports false positive when payload parsing fails"
}
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Sightings
| Author | Source | Type | Date |
|---|
Nomenclature
- Seen: The vulnerability was mentioned, discussed, or observed by the user.
- Confirmed: The vulnerability has been validated from an analyst's perspective.
- Published Proof of Concept: A public proof of concept is available for this vulnerability.
- Exploited: The vulnerability was observed as exploited by the user who reported the sighting.
- Patched: The vulnerability was observed as successfully patched by the user who reported the sighting.
- Not exploited: The vulnerability was not observed as exploited by the user who reported the sighting.
- Not confirmed: The user expressed doubt about the validity of the vulnerability.
- Not patched: The vulnerability was not observed as successfully patched by the user who reported the sighting.
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