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

Analyzed

AliasesUBUNTU-CVE-2026-39984DEBIAN-CVE-2026-39984CGA-2442-2c6f-xjwq+319 more

Published 14-04-2026Last modified 16-04-2026

Vulnerability summary

CVE-2026-39984 is a medium (CVSS 5.5) Improper Certificate Validation vulnerability in linuxfoundation sigstore_timestamp_authority. EPSS estimates a 0.10% chance of exploitation in the next 30 days, higher than 0.7% of scored vulnerabilities.

Priority

Routine

Not severe (CVSS 5.5, local access); no exploitation reported by the 5 checked sources

Source freshness unavailable

How is this decided?

CVSS score

5.5/10

010

Medium · v3.1 (CVE.org)

EPSS score

0.10%

0%100%

Low · -0.01 pp in 30 days

KEVNot listedNot listed by any tracked catalog.

RansomwareNot flaggedNo ransomware use recorded.

Public exploits0No public exploits recorded

Advisory lineage

Upstream 0 · Downstream 14 · Related 15

OPENSUSE-SU-2026:10651-1 OPENSUSE-SU-2026:10702-1 OPENSUSE-SU-2026:11144-1 OPENSUSE-SU-2026:21060-1 OPENSUSE-SU-2026:21483-1 OPENSUSE-SU-2026:22158-1+9 more

Timeline

14-04-2026
PublishedVulnerability first disclosed.
16-04-2026
Last modifiedVulnerability information updated.

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.

CVSS metrics

7 scores · 7 sources · 1 version

v3.15.5

EPSS trend

Probability

0.10%

Chance of exploitation in the next 30 days

Percentile

Versus all other CVEs

30-day change

Decrease -0.01 pp

From 0.11% on 04-10-2026

04-10-202603-11-2026

Known exploited

Compare KEV catalogs

CISA KEV

Not in the CISA KEV catalog.

ENISA CNW

Not in the ENISA CNW catalog.

CIRCL

Not in the CIRCL catalog.

Public exploits

0 found

No public exploits indexed.

Weaknesses

CWE · root cause

CWE-295Improper Certificate ValidationThe product does not validate, or incorrectly validates, a certificate.

Affected systems

Version check

Known conditions: local access, no authentication, user interaction (CVSS vector). Other conditions: not stated in public data.

Chainguard160 products

aactl< 0.4.12-r50
buildkitd< 0.29.0-r6
buildkitd-fips< 0.29.0-r3
cg< 0.2.245-r0
chainctl< 0.2.249-r1

chainctl-fips< 0.2.249-r1
cloudbeat-8.17< 8.17.10-r27
cloudbeat-9.0< 9.0.8-r30
cloudbeat-9.1< 9.1.10-r24
cloudbeat-9.2< 9.2.8-r11
cloudbeat-9.3< 9.3.3-r4
cloudbeat-fips-8.17< 8.17.10-r32
cloudbeat-fips-9.0< 9.0.8-r34
cloudbeat-fips-9.1< 9.1.10-r26
cloudbeat-fips-9.2< 9.2.8-r9
cloudbeat-fips-9.3< 9.3.2-r8
cloudbeat-fips-9.4< 9.4.0-r3
commercial-chainloop-backend< 1.61.1-r0
commercial-kyverno-1.14All versions (No fix recorded)
commercial-kyverno-1.15All versions (No fix recorded)
commercial-kyverno-1.16All versions (No fix recorded)
commercial-kyverno-1.17< 1.17.2-r0
commercial-kyverno-background-controller-1.14All versions (No fix recorded)
commercial-kyverno-background-controller-1.15All versions (No fix recorded)
commercial-kyverno-background-controller-1.16All versions (No fix recorded)
commercial-kyverno-background-controller-1.17< 1.17.2-r0
commercial-kyverno-cleanup-controller-1.14All versions (No fix recorded)
commercial-kyverno-cleanup-controller-1.15All versions (No fix recorded)
commercial-kyverno-cleanup-controller-1.16All versions (No fix recorded)
commercial-kyverno-cleanup-controller-1.17< 1.17.2-r0
commercial-kyverno-reports-controller-1.14All versions (No fix recorded)
commercial-kyverno-reports-controller-1.15All versions (No fix recorded)
commercial-kyverno-reports-controller-1.16All versions (No fix recorded)
commercial-kyverno-reports-controller-1.17< 1.17.2-r0
commercial-kyvernopre-1.14All versions (No fix recorded)
commercial-kyvernopre-1.15All versions (No fix recorded)
commercial-kyvernopre-1.16All versions (No fix recorded)
commercial-kyvernopre-1.17< 1.17.2-r0
cosign< 3.0.5-r9
cosign-fips< 3.0.5-r7
crossplane-1.20< 1.20.7-r1
crossplane-2.0< 2.0.7-r10
crossplane-2.1< 2.1.4-r11
crossplane-2.2< 2.2.0-r8
crossplane-2.2-crank< 2.2.0-r8
crossplane-fips-1.20< 1.20.7-r1
crossplane-fips-2.0< 2.0.7-r12
crossplane-fips-2.1< 2.1.4-r12
crossplane-fips-2.2< 2.2.0-r10
crossplane-fips-2.2-crank< 2.2.0-r10
docker-cli-buildx< 0.33.0-r5
docker-cli-buildx-fips< 0.33.0-r7
dockerd-29< 29.4.1-r0
falcoctl< 0.12.2-r10
falcoctl-fips< 0.12.2-r8
flux-source-controller< 1.8.2-r4
flux-source-controller-fips< 1.8.2-r5
gh< 2.90.0-r0
gitsign< 0.14.0-r17
goreleaser< 2.15.3-r1
image-factory< 1.0.3-r6
image-factory-fips< 1.0.3-r9
jfrog-cli< 2.100.0-r1
ko< 0.18.1-r12
ko-fips< 0.18.1-r13
kubescape< 4.0.5-r0
kubescape-server< 4.0.5-r0
kubescape-server-downloader< 4.0.5-r0
kubescape-server-fips< 4.0.5-r0
kubescape-server-fips-downloader< 4.0.5-r0
kyverno-1.14< 1.14.5-r12
kyverno-1.15< 1.15.3-r24
kyverno-1.16< 1.16.4-r1
kyverno-1.17< 1.17.1-r15
kyverno-background-controller-1.14< 1.14.5-r12
kyverno-background-controller-1.15< 1.15.3-r24 | < 1.15.3-r23
kyverno-background-controller-1.16< 1.16.4-r1
kyverno-background-controller-1.17< 1.17.1-r15
kyverno-background-controller-fips-1.14< 1.14.5-r12
kyverno-background-controller-fips-1.15< 1.15.20-r8
kyverno-background-controller-fips-1.16< 1.16.4-r1
kyverno-background-controller-fips-1.17< 1.17.1-r13
kyverno-cleanup-controller-1.14< 1.14.5-r12
kyverno-cleanup-controller-1.15< 1.15.3-r23
kyverno-cleanup-controller-1.16< 1.16.4-r1
kyverno-cleanup-controller-1.17< 1.17.1-r15
kyverno-cleanup-controller-fips-1.14< 1.14.5-r12
kyverno-cleanup-controller-fips-1.15< 1.15.20-r8 | < 1.15.20-r9
kyverno-cleanup-controller-fips-1.16< 1.16.4-r1
kyverno-cleanup-controller-fips-1.17< 1.17.1-r13
kyverno-cli-1.14< 1.14.5-r12
kyverno-cli-1.15< 1.15.3-r24
kyverno-cli-1.16< 1.16.4-r1
kyverno-cli-1.17< 1.17.1-r15
kyverno-cli-fips-1.14< 1.14.5-r12
kyverno-cli-fips-1.15< 1.15.20-r9 | < 1.15.20-r8
kyverno-cli-fips-1.16< 1.16.4-r1
kyverno-cli-fips-1.17< 1.17.1-r13
kyverno-fips-1.14< 1.14.5-r12
kyverno-fips-1.15< 1.15.20-r9
kyverno-fips-1.16< 1.16.4-r1
kyverno-fips-1.17< 1.17.1-r13
kyverno-init-container-1.14< 1.14.5-r12
kyverno-init-container-1.15< 1.15.3-r23 | < 1.15.3-r24
kyverno-init-container-1.16< 1.16.4-r1
kyverno-init-container-1.17< 1.17.1-r15
kyverno-init-container-fips-1.14< 1.14.5-r12
kyverno-init-container-fips-1.15< 1.15.20-r9 | < 1.15.20-r8
kyverno-init-container-fips-1.16< 1.16.4-r1
kyverno-init-container-fips-1.17< 1.17.1-r13
kyverno-notation-aws< 1.1-r50
kyverno-notation-aws-fips< 1.1-r46
kyverno-policy-reporter-plugins-kyverno< 0.6.0-r4
kyverno-policy-reporter-plugins-kyverno-fips< 0.6.0-r3
kyverno-reports-controller-1.14< 1.14.5-r12
kyverno-reports-controller-1.15< 1.15.3-r23
kyverno-reports-controller-1.16< 1.16.4-r1
kyverno-reports-controller-1.17< 1.17.1-r15
kyverno-reports-controller-fips-1.14< 1.14.5-r12
kyverno-reports-controller-fips-1.15< 1.15.20-r8 | < 1.15.20-r9
kyverno-reports-controller-fips-1.16< 1.16.4-r1
kyverno-reports-controller-fips-1.17< 1.17.1-r13
neuvector-sigstore-interface< 0_git20260405-r1
policy-controller< 0.15.1-r4
policy-controller-fips< 0.15.1-r2
policy-controller-tester< 0.15.1-r4
policy-controller-tester-fips< 0.15.1-r2
ratify< 1.4.0-r36
ratify-fips< 1.4.0-r35
ratify-licensechecker-compat< 1.4.5-r4
reports-serverAll versions (No fix recorded)
sigstore-scaffolding-fips-tsa-createcertchain< 0.7.31-r10
sigstore-scaffolding-fips-tuf-server< 0.7.31-r10
sigstore-scaffolding-tsa-createcertchain< 0.7.31-r12
sigstore-scaffolding-tuf-server< 0.7.31-r12
skaffold< 2.18.3-r2
skaffold-fips< 2.18.3-r1
slsa-verifier< 2.7.1-r23
spire-agent< 1.14.5-r2
spire-agent-fips< 1.14.5-r1
tekton-chains< 0.26.2-r8
tekton-chains-fips< 0.26.2-r10
teleport-18.6< 18.6.8-r29
teleport-18.6-kube-agent-updater< 18.6.8-r29
teleport-18.6-operator< 18.6.8-r29
teleport-operator-fips-17< 17.7.23-r0
teleport-operator-fips-18< 18.7.5-r0
tflint< 0.61.0-r10
tflint-fips< 0.61.0-r10
tkn< 0.44.1-r3
tkn-fips< 0.44.1-r3
trivy< 0.69.3-r12
trivy-fips< 0.69.3-r7
trivy-operator< 0.30.1-r6
trivy-operator-fips< 0.30.1-r5
vexctl< 0.4.1-r19
witness< 0.10.2-r20
zarf< 0.74.2-r6
zarf-fips< 0.74.2-r5
zot< 2.1.16-r0

Show all 160

Wolfi40 products

aactl< 0.4.12-r50
buildkitd< 0.29.0-r6
cosign< 3.0.5-r9
crossplane-2.1< 2.1.4-r11
crossplane-2.2< 2.2.0-r8

Show all 40

2 vendors · 200 products · Showing 200 of 216

References

8 links

github.com/sigstore/timestamp-authority/security/advisories/GHSA-xm5m-wgh2-rrg3X Refsource CONFIRMREPORTAdvisoryWEBMitigationVendor Advisory
github.com/sigstore/timestamp-authority/releases/tag/v2.0.6X Refsource MISCWEBProductRelease Notes
ubuntu.com/security/CVE-2026-39984REPORT
www.cve.org/CVERecord?id=CVE-2026-39984REPORT
security-tracker.debian.org/tracker/CVE-2026-39984Advisory
github.com/CVEProject/cvelistV5/tree/main/cves/2026/39xxx/CVE-2026-39984.jsonAdvisory
nvd.nist.gov/vuln/detail/CVE-2026-39984Advisory
github.com/sigstore/timestamp-authorityPACKAGE