CVE-2025-66564VulnerabilityPublished 4 Dec 2025

CVE-2025-66564: sigstore timestamp-authority · Asymmetric Resource Consumption (Amplification)

Affects sigstore timestamp-authoritySource CVE Database V5

Not known to be exploited · CVSS 7.5 High : upgrade to 2.0.3 soon.

Data as of 26 Oct 2026, 06:26 UTC

CVSS 3.1 base score

7.5High

How severe the flaw is on the 0–10 CVSS scale.

EPSS: 0.4% chance of exploitation in 30 days – higher than 38% of CVEsExploit Prediction Scoring System: the likelihood attackers will use this flaw soon.
Patch: Available – fixed in 2.0.3

CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H

Attack Vector: Network
Attack Complexity: Low
Privileges Required: None
User Interaction: None
Scope: Unchanged
Confidentiality: None
Integrity: None
Availability: High

Bold values are the worst case: easiest to exploit or largest impact.

Attack Vector: Network: The vulnerable component is bound to the network stack and the set of possible attackers extends beyond the other options listed, up to and including the entire Internet. Such a vulnerability is often termed 'remotely exploitable' and can be thought of as an attack being exploitable at the protocol level one or more network hops away (e.g., across one or more routers).
Attack Complexity: Low: Specialized access conditions or extenuating circumstances do not exist. An attacker can expect repeatable success against the vulnerable component.
Privileges Required: None: The attacker is unauthorized prior to attack, and therefore does not require any access to settings or files to carry out an attack.
User Interaction: None: The vulnerable system can be exploited without any interaction from any user.
Scope: Unchanged: An exploited vulnerability can only affect resources managed by the same security authority. In this case, the vulnerable component and the impacted component are either the same, or both are managed by the same security authority.
Confidentiality: None: There is no loss of confidentiality within the impacted component.
Integrity: None: There is no loss of integrity within the impacted component.
Availability: High: There is total loss of availability, resulting in the attacker being able to fully deny access to resources in the impacted component; this loss is either sustained (while the attacker continues to deliver the attack) or persistent (the condition persists even after the attack has completed). Alternatively, the attacker has the ability to deny some availability, but the loss of availability presents a direct, serious consequence to the impacted component (e.g., the attacker cannot disrupt existing connections, but can prevent new connections; the attacker can repeatedly exploit a vulnerability that, in each instance of a successful attack, leaks a only small amount of memory, but after repeated exploitation causes a service to become completely unavailable).

Definitions: FIRST CVSS v3.1 specification.

Exploitation evidence

Disclosed: evidence found.
CVE published 4 Dec 2025
Detectable: no evidence on record.
No public nuclei template indexed
Weaponised: no evidence on record.
No public exploit code indexed in Metasploit or Exploit-DB
Exploited in the wildExploited: no evidence on record.
Not in CISA KEV and no source reports exploitation
Observed by OffSeq MirageSeen by Mirage: no evidence on record.
No attack traffic recorded by OffSeq Mirage sensors

A missing step is not evidence of safety. Sources: cve.org (opens in a new tab), the Metasploit, Exploit-DB and nuclei-templates index as of 2026-10-26.

Disclosed: The CVE record is public on cve.org. Its publication is t = 0.
Detectable: A public nuclei template can find exposed instances, for defenders and attackers alike.
Weaponised: Public exploit code exists in Metasploit or Exploit-DB, or CISA SSVC reports a public proof of concept.
Exploited in the wild: CISA KEV lists it, CISA SSVC rates exploitation active, or a source reports attacks.
Observed by OffSeq Mirage: OffSeq Mirage honeypot sensors recorded attack traffic for this CVE, or found exposed hosts without attack traffic.

Moments are spaced evenly, not to scale; a dashed line marks a gap of six months or more. Deltas count from t = 0. Sources that give only a date (CISA KEV, Exploit-DB, or a time of exactly 00:00Z) read “same day” rather than hours. Metasploit modules carry the flaw’s disclosure date, not their release date, and nuclei templates carry no date, so both appear above but not on the timeline.

What to do

Upgrade sigstore/timestamp-authority to 2.0.3.

Affected software

Product	Affected	Fixed in
GitHubsigstore/timestamp-authority`pkg:github/sigstore/timestamp-authority`Other threats	Affected <2.0.3	Fixed in 2.0.3

Check your own hosts for these packages with threat-finder (opens in a new tab), our free open-source scanner.

AI-suggested

European organizations should immediately upgrade all instances of sigstore timestamp-authority to version 2.0.3 or later, where this vulnerability is fixed. Until patching is complete, implement network-level protections such as rate limiting and input validation proxies to detect and block anomalously large or malformed OID and Content-Type header values. Monitoring and alerting on unusual spikes in memory or CPU usage on timestamp-authority servers can provide early warning of exploitation attempts. Employ Web Application Firewalls (WAFs) configured to inspect and limit header lengths and payload sizes. Incorporate this vulnerability into incident response playbooks to quickly isolate affected services if exploitation is suspected. Finally, review and harden software supply chain security policies to ensure timely updates of critical infrastructure components.

Description

Sigstore Timestamp Authority is a service for issuing RFC 3161 timestamps. Prior to 2.0.3, 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). This vulnerability is fixed in 2.0.3.

Impact

For European organizations, the primary impact of CVE-2025-66564 is the risk of denial-of-service attacks against infrastructure components relying on the sigstore timestamp-authority service. This service is critical in software supply chain security, providing trusted timestamps for code signing and artifact verification. Disruption could delay or block software deployment pipelines, impacting development velocity and operational continuity. Organizations heavily invested in open source software development, continuous integration/continuous deployment (CI/CD) pipelines, or those that integrate sigstore for artifact verification are at heightened risk. The attack requires no authentication, increasing the threat surface. While no data confidentiality or integrity is compromised, availability degradation can have cascading effects on business operations and trust in software provenance. Additionally, the vulnerability could be leveraged as part of a broader attack chain targeting software supply chains, which are strategic assets in Europe’s digital economy.

Summary

CVE-2025-66564 is a vulnerability classified under CWE-405 (Asymmetric Resource Consumption) affecting the sigstore timestamp-authority service, which issues RFC 3161 timestamps used in software supply chain security. The root cause lies in the handling of untrusted input data in two functions: api.ParseJSONRequest and api.getContentType. Specifically, api.ParseJSONRequest processes an optionally provided OID string by splitting it on periods using strings.Split, while api.getContentType splits the Content-Type header on an application string. Both inputs are attacker-controlled and can be crafted to contain excessively long strings with many delimiters. This causes the functions to allocate memory linearly proportional to the input length (O(n)), which can be exploited to consume disproportionate server resources. The vulnerability impacts availability by enabling denial-of-service attacks through resource exhaustion. It does not affect confidentiality or integrity, requires no privileges or user interaction, and can be triggered remotely over the network. The vulnerability was addressed and fixed in sigstore timestamp-authority version 2.0.3. No known exploits are currently reported in the wild, but the high CVSS score (7.5) reflects the ease of exploitation and potential impact on service availability.

CWE-405Asymmetric Resource Consumption (Amplification) (opens in a new tab)
Class weakness
The product does not properly control situations in which an adversary can cause the product to consume or produce excessive resources without requiring the adversary to invest equivalent work or otherwise prove authorization, i.e., the adversary's influence is "asymmetric."
Architecture and Design
An application must make resources available to a client commensurate with the client's access level.
Architecture and Design
An application must, at all times, keep track of allocated resources and meter their usage appropriately.
System Configuration
Consider disabling resource-intensive algorithms on the server side, such as Diffie-Hellman key exchange.
OWASP Cheat Sheets
File Upload (opens in a new tab)
OWASP ASVS 4.0.3
V12.1.1 (opens in a new tab)
From MITRE CWE, MITRE CAPEC and OWASP (Top 10, OpenCRE).

References

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Exploitation evidence

What to do

Affected software

Description

AI analysisMachine-generated, updated 12 Dec 2025, 00:13 UTC

WeaknessesCWE-405

Technical details

References

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