How severe is CVE-2025-66564?

CVE-2025-66564 has a CVSS score of 7.5/10, rated HIGH. Immediate patching is strongly recommended.

Which packages are affected by CVE-2025-66564?

CVE-2025-66564 affects the following packages: github.com/sigstore/timestamp-authority (Go). Ecosystems affected: Go.

How do I fix CVE-2025-66564?

Update github.com/sigstore/timestamp-authority to 2.0.3 or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms CVE-2025-66564 is resolved across your whole dependency graph.

How do I detect CVE-2025-66564 in my Go dependencies?

Scan your dependency tree (package-lock.json, pnpm-lock.yaml, requirements.txt, go.sum, etc.) for github.com/sigstore/timestamp-authority, including transitive dependencies — a direct dependency you never call can still pull in a vulnerable version.

How do I mitigate CVE-2025-66564 if there is no patch (or I can't update yet)?

Cap what an attacker can consume: apply request size, rate and timeout limits in front of the affected component, and run it with memory and CPU limits so exhaustion degrades one worker rather than the whole service.

Is CVE-2025-66564 actively exploited in the wild?

No public exploit code has been indexed for CVE-2025-66564 yet. This does not mean the vulnerability cannot be exploited — absence of public exploits does not imply safety. Apply the recommended fix and use O3 Security to monitor your exposure.

What is the EPSS score for CVE-2025-66564?

CVE-2025-66564 has an EPSS (Exploit Prediction Scoring System) score of 0.5%, placing it in the 41th percentile of all CVEs. EPSS is maintained by FIRST.org and estimates the probability that a vulnerability will be exploited in the wild within the next 30 days. This score indicates relatively lower exploitation probability, though the CVSS severity should still guide your patching priority.

What type of vulnerability is CVE-2025-66564?

CVE-2025-66564 is classified as CWE-405 (CWE-405). This weakness type describe the underlying flaw category, which helps determine the potential impact and the right class of mitigation.

When was CVE-2025-66564 published, and has it been updated?

CVE-2025-66564 was published on December 4, 2025 and was last updated on October 28, 2026. Advisory data evolves as severity scores, affected ranges, and exploit intelligence are revised — always check the latest version of the advisory before acting.

🐹

🐹 Go

Not in CISA KEV

HIGH severity

CVE-2025-66564 — timestamp-authority

HIGHFix: sigstore/timestamp-authority@0cae34e

CVE-2025-66564 is a high-severity (CVSS 7.5) CWE-405 vulnerability in github.com/sigstore/timestamp-authority. A fix is available for github.com/sigstore/timestamp-authority — see the affected versions and patch details below.

Sigstore Timestamp Authority allocates excessive memory during request parsing

Also known asGHSA-4qg8-fj49-pxjhGO-2025-4192

Published

Dec 4, 2025

Updated

Oct 28, 2026

Affected

1 pkg

Patched

1 / 1

Exploits

None indexed

Exploitation data as of Nov 10, 2026 · OSV.dev, NVD, FIRST.org (EPSS)

Exploitation Status

No confirmed exploitation observed yet

CISA assesses this as automatable — exploitation doesn’t require manual, per-target effort, which raises the odds of mass scanning and opportunistic attacks.
CISA’s own triage has not observed active exploitation or public proof-of-concept code for this CVE as of its last assessment.

Exploitation and automatability from CISA’s SSVC triage for CVE-2025-66564.

EPSS Exploitation Probability

via FIRST.org ↗

0.5%probability of exploitation in next 30 days

Lower Risk+0.03%

Lower risk than most CVEs41th percentile — riskier than 41% of all scored CVEsHighest risk

Probability of exploitation in the next 30 days, from FIRST.org EPSS.

How urgent is this, really

Where this sits among everything scored

Real-World Exposure

1 pkg affected

🐹github.com/sigstore/timestamp-authority

Real-time download stats are indexed for npm and PyPI packages. This vulnerability affects Go packages — download data is not available via public APIs for these ecosystems.

Description

Impact

Excessive memory allocation

Function api.ParseJSONRequest currently splits (via a call to strings.Split) an optionally-provided OID (which is untrusted data) on periods. Similarly, function api.getContentType splits the Content-Type header (which is also untrusted data) on an application string.

As a result, in the face of a malicious request with either an excessively long OID in the payload containing many period characters or a malformed Content-Type header, a call to api.ParseJSONRequest or api.getContentType incurs allocations of O(n) bytes (where n stands for the length of the function's argument). Relevant weakness: CWE-405: Asymmetric Resource Consumption (Amplification)

Patches

Upgrade to v2.0.3.

Workarounds

There are no workarounds with the service itself. If the service is behind a load balancer, configure the load balancer to reject excessively large requests.

Affected Packages

1 total 1 fixed

Ecosystem	Package	Vulnerable range	Fix
🐹Go	`github.com/sigstore/timestamp-authority`	all versions	2.0.3`go get github.com/sigstore/timestamp-authority@v2.0.3`

Affected Products

1 product · 1 configurations

Application

sigstore timestamp authoritylinuxfoundation

< 2.0.3

range

Detection & mitigation playbook

Open-source dependency

Detect
Scan your dependency tree (package-lock.json, pnpm-lock.yaml, requirements.txt, go.sum, etc.) for github.com/sigstore/timestamp-authority, including transitive dependencies — a direct dependency you never call can still pull in a vulnerable version.
Fix
Update github.com/sigstore/timestamp-authority to 2.0.3 or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms CVE-2025-66564 is resolved across your whole dependency graph.
Workarounds
Cap what an attacker can consume: apply request size, rate and timeout limits in front of the affected component, and run it with memory and CPU limits so exhaustion degrades one worker rather than the whole service.

Fixing This On Your OS

If you run this on a Linux distribution, patch through your package manager against the distro's own security advisory below — it tracks the exact backported fix for your release, which can ship on a different timeline (and sometimes a different severity) than the upstream project.

Red HatImportant

This vulnerability is rated Important for Red Hat products. The Sigstore Timestamp Authority, a service for issuing RFC 3161 timestamps, is prone to excessive memory allocation. This occurs when processing untrusted OID payloads with many period characters or malformed Content-Type headers. An unauthenticated attacker…

Product	Fixed in	Advisory
OpenShift Security Profiles Operator 1	`compliance/openshift-security-profiles-operator-bundle:1771367226`	RHSA-2026:2852
Red Hat Advanced Cluster Security 4.8	`advanced-cluster-security/rhacs-main-rhel8:1769615659`	RHSA-2026:1517
Red Hat Advanced Cluster Security 4.9	`advanced-cluster-security/rhacs-main-rhel8:1770250889`	RHSA-2026:2350
Red Hat Advanced Cluster Security 4.9	`advanced-cluster-security/rhacs-main-rhel8:1770074713`	RHSA-2026:2568
Red Hat OpenShift Pipelines 1.15	`openshift-pipelines/pipelines-chains-controller-rhel8:1772093872`	RHSA-2026:3710
Red Hat OpenShift Pipelines 1.15	`openshift-pipelines/pipelines-chains-controller-rhel8:1772093872`	RHSA-2026:3712
Red Hat OpenShift Pipelines 1.20	`openshift-pipelines/pipelines-chains-controller-rhel9:1771374749`	RHSA-2026:3825
Red Hat OpenShift Pipelines 1.20	`openshift-pipelines/pipelines-cli-tkn-rhel9:1772694865`	RHSA-2026:3827

Frequently Asked Questions

### Impact **Excessive memory allocation** Function [api.ParseJSONRequest](https://github.com/sigstore/timestamp-authority/blob/26d7d426d3000abdbdf2df34de56bb92246c0365/pkg/api/timestamp.go#L63) currently splits (via a call to [strings.Split](https://pkg.go.dev/strings#Split)) an optionally-provided OID (which is untrusted data) on periods. Similarly, function [api.getContentType](https://github.com/sigstore/timestamp-authority/blob/26d7d426d3000abdbdf2df34de56bb92246c0365/pkg/api/timestamp.go#L114) splits the `Content-Type` header (which is also untrusted data) on an `application` string.