VulnerabilityPublished 7 Apr 2026

CVE-2026-39395: sigstore cosign · Unchecked Error Condition

Affects sigstore cosignSource CVE Database V5

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Not known to be exploited · CVSS 4.3 Medium : upgrade to 3.0.6 or 2.6.3 when convenient.

Data as of 30 Oct 2026, 06:59 UTC

CVSS 3.1 base score

4.3Medium

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

EPSS: 0.2% chance of exploitation in 30 days – higher than 15% of CVEsExploit Prediction Scoring System: the likelihood attackers will use this flaw soon.
Patch: Available – fixed in 3.0.6, 2.6.3

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

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

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: Required: Successful exploitation of this vulnerability requires a user to take some action before the vulnerability can be exploited.
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: Low: Modification of data is possible, but the attacker does not have control over the consequence of a modification, or the amount of modification is limited. The data modification does not have a direct, serious impact on the impacted component.
Availability: None: There is no impact to availability within the impacted component.

Definitions: FIRST CVSS v3.1 specification.

Exploitation evidence

Disclosed: evidence found.
CVE published 7 Apr 2026
Detectable: no evidence on record.
No public nuclei template indexed
Weaponized: 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 29 Oct 2026.

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.
Weaponized: A Metasploit exploit module or Exploit-DB entry exists (Metasploit scanner modules do not count), or CISA SSVC or the CVSS exploit maturity 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 cosign to 3.0.6 or 2.6.3; sigstore/cosign to 2.6.3.

Affected software

Product	Affected	Fixed in
sigstorecosign	Affected >=3.0.0 <3.0.6	Fixed in 3.0.6
sigstorecosign	Affected <2.6.3	Fixed in 2.6.3
GitHubsigstore/cosign`pkg:github/sigstore/cosign`Other threats	Affected <2.6.3	Fixed in 2.6.3

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

AI-suggested

Upgrade cosign to version 3.0.6 or later, or 2.6.3 or later, where this vulnerability is fixed. Patch status is confirmed by the version information in the advisory. No additional mitigation is indicated.

Description

Cosign versions prior to 3.0.6 and 2.6.3 contain a vulnerability where the verify-blob-attestation command may incorrectly report a successful verification for attestations with malformed payloads or mismatched predicate types. This occurs due to improper error handling and bypass of predicate type validation in different bundle formats. The issue is fixed in versions 3.0.6 and 2.6.

Impact

The vulnerability may cause cosign to incorrectly verify attestations that have malformed payloads or mismatched predicate types, potentially undermining the integrity of the verification process. There is no impact on confidentiality or availability. No known exploits are reported in the wild.

Summary

The vulnerability in sigstore's cosign affects the verify-blob-attestation functionality, where malformed or mismatched attestation payloads can be erroneously accepted as valid. For old-format bundles and detached signatures, a logic flaw in error handling caused this incorrect verification. For new-format bundles, predicate type validation was completely bypassed. This improper check for unusual or exceptional conditions (CWE-754) could lead to false positive verification results. The flaw is resolved in cosign versions 3.0.6 and 2.6.3.

CWE-754Improper Check for Unusual or Exceptional Conditions (opens in a new tab)
Class weaknessLikelihood of exploit: MediumOWASP Top 10 A10:2025: Mishandling of Exceptional Conditions (opens in a new tab)
The product does not check or incorrectly checks for unusual or exceptional conditions that are not expected to occur frequently during day to day operation of the product.
Requirements · Language Selection
Use a language that does not allow this weakness to occur or provides constructs that make this weakness easier to avoid.
Implementation
Check the results of all functions that return a value and verify that the value is expected.
Implementation
If using exception handling, catch and throw specific exceptions instead of overly-general exceptions (CWE-396, CWE-397). Catch and handle exceptions as locally as possible so that exceptions do not propagate too far up the call stack (CWE-705). Avoid unchecked or uncaught exceptions where feasible (CWE-248).
OWASP Cheat Sheets
Logging (opens in a new tab)
Error Handling (opens in a new tab)
OWASP ASVS 4.0.3
V11.1.7 (opens in a new tab)
From MITRE CWE, MITRE CAPEC and OWASP (Top 10, OpenCRE).

References

github.com/sigstore/cosign/security/advisories/GHSA-w6c6-c85g-mmv6 (opens in a new tab)

Community reviews

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Exploitation evidence

What to do

Affected software

Description

AI analysisMachine-generated, updated 15 Apr 2026, 15:54 UTC

WeaknessesCWE-754

Technical details

References

Community reviews

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