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Fencer Intel
medium 4.3

CVE-2026-39395 json

Cosign's verify-blob-attestation reports false positive when payload parsing fails

published 7mo ago modified last mo. also BIT-cosign-2026-39395 , EUVD-2026-19919 , GHSA-w6c6-c85g-mmv6 , GO-2026-5694

cvss
4.3
version 3.1, CNA
cisa kev
Not listed
not in CISA's catalog
epss
0.3%
EPSS 0.3% chance of exploitation in 30 days, percentile 16%
public exploits
0
none known

Summary

Cosign provides code signing and transparency for containers and binaries. Prior to 3.0.6 and 2.6.3, 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. This vulnerability is fixed in 3.0.6 and 2.6.3.

Patch / fix

  • go github.com/sigstore/cosign 2.6.3, 3.0.6
  • bitnami cosign 2.6.3, 3.0.6
  • go github.com/sigstore/cosign/v2 2.6.3
  • go github.com/sigstore/cosign/v3 3.0.6
  • sigstore cosign 2.6.3, 3.0.6
  • cosign Debian 14 2.6.3-1

debian advisories DEBIAN-CVE-2026-39395

  • cosign SLES for SAP applications 16.0, SLES 16.0 3.0.6-160000.1.1
  • cosign SLE Module for Basesystem 15 SP7 3.0.6-150400.3.42.1

suse advisories SUSE-SU-2026:22344-1SUSE-SU-2026:2365-1

  • govulncheck-vulndb openSUSE Leap 16.0 0.0.20260723T184607-160000.1.1
  • cosign openSUSE Leap 16.0 3.0.6-160000.1.1
  • cosign openSUSE Tumbleweed 3.0.6-1.1

opensuse advisories openSUSE-SU-2026:21483-1openSUSE-SU-2026:21036-1openSUSE-SU-2026:10753-1

  • cosign Alpine 3.23 2.6.3-r0
  • cosign Alpine 3.24 3.0.6-r0

alpine advisories ALPINE-CVE-2026-39395

Alpine secdb © Alpine Linux, from https://secdb.alpinelinux.org via OSV; changed: normalised to fixed package versions per release. CC BY-SA 4.0

Is CVE-2026-39395 in your dependencies? Fencer shows which of your repositories are affected as soon as an advisory lands, and opens the fix as a pull request.

Check with Fencer

Vendor advisories

What the vendors themselves say about their products: affected, fixed or not affected, and what to do.

red hat product security vex CVE-2026-39395 updated cvss 6.5

github.com/sigstore/cosign: Cosign: Incorrect attestation verification due to malformed payloads or mismatched predicate types

  • Red Hat OpenShift Pipelines openshift-pipelines-client, redhat-user-workloads/tekton-ecosystem-tenant/1-20/opc-rhel9, redhat-user-workloads/tekton-ecosystem-tenant/1-15/cli-tkn-rhel8, redhat-user-workloads/tekton-ecosystem-tenant/1-20/cli-tkn-rhel9, redhat-user-workloads/tekton-ecosystem-tenant/pipelines-opc-rhel9, redhat-user-workloads/tekton-ecosystem-tenant/pipelines-cli-tkn-rhel9, +5 more Red Hat OpenShift Serverless redhat-user-workloads/ocp-serverless-tenant/serverless-operator-137/kn-plugin-event-sender Red Hat Advanced Cluster Security 4 rhacs-eng/release-main, rhacs-eng/release-roxctl, rhacs-eng/release-operator, rhacs-eng/release-scanner-v4 Red Hat Trusted Artifact Signer securesign/gitsign, securesign/cli-cosign, securesign/policy-controller, redhat-user-workloads/rhtap-contract-tenant/ec-v06/cli-v06, redhat-user-workloads/rhtap-contract-tenant/ec-v07/cli-v07, redhat-user-workloads/rhtap-contract-tenant/ec-v08/cli-v08 Red Hat Security Profiles Operator redhat-user-workloads/ocp-isc-tenant/security-profiles-operator-release, redhat-user-workloads/ocp-isc-tenant/security-profiles-operator-bundle-release Red Hat Zero Trust Workload Identity Manager redhat-user-workloads/zero-trust-workload-tenant/spiffe-spire-agent-1-13-3/spiffe-spire-agent-1-13-3, redhat-user-workloads/zero-trust-workload-tenant/spiffe-spire-server-1-13-3/spiffe-spire-server-1-13-3, redhat-user-workloads/zero-trust-workload-tenant/spiffe-spire-oidc-discovery-provider-1-13-3/spiffe-spire-oidc-discovery
    +1 more products
    Red Hat Zero Trust Workload Identity Manager - Tech Preview redhat-user-workloads/zero-trust-workload-tenant/spiffe-spire-agent-1-12-4/spiffe-spire-agent-1-12-4, redhat-user-workloads/zero-trust-workload-tenant/spiffe-spire-server-1-12-4/spiffe-spire-server-1-12-4, redhat-user-workloads/zero-trust-workload-tenant/zero-trust-workload-identity-manager-0-2/zero-trust-workload-identity-m, redhat-user-workloads/zero-trust-workload-tenant/spiffe-spire-oidc-discovery-provider-1-12-4/spiffe-spire-oidc-discovery, redhat-user-workloads/zero-trust-workload-tenant/zero-trust-workload-identity-manager-bundle-0-2/zero-trust-workload-ide
    affected: workaround, no fix available “Fix deferred”

Red Hat CSAF VEX © Red Hat, Inc., from https://security.access.redhat.com/data/csaf/v2/vex/; changed: reduced to product statuses and remediations. CC BY 4.0 · csaf

CISA SSVC

Exploitation
none
Automatable
no
Technical impact
partial
Assessed
7mo ago

Exploit prediction

0.25% chance of exploitation in the next 30 days, higher than 16% of all scored CVEs (FIRST EPSS, 2026-11-09).

CVSS scores

assigned by version score vector
CNA 3.1 4.3 CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:N/I:L/A:N
GitHub 3.1 4.3 CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:N/I:L/A:N
NVD 3.1 5.3 CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:L/A:N
OSV 3.1 5.3 CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:L/A:N

Affected packages

ecosystem package affected fixed in
go github.com/sigstore/cosign
>=3.0.0, <3.0.6
<2.6.3
all versions
3.0.6
2.6.3
bitnami cosign
<2.6.3
>=3.0.0, <3.0.6
2.6.3
3.0.6
go github.com/sigstore/cosign/v2
<2.6.3
2.6.3
go github.com/sigstore/cosign/v3
>=3.0.0, <3.0.6
3.0.6

Affected products

  • sigstore cosign

Classification

Weakness
  • CWE-754 Improper Check for Unusual or Exceptional Conditions

References

Sources

Fencer Intel keeps one entry per vulnerability: the CVE id wins, then GHSA, and records that alias each other are merged, except that two CVEs always keep separate entries. The same data is available as JSON.

CPEs and fixed versions use Anchore's correction of NVD's data: Added CPE configurations because not yet analyzed by NVD.