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Crossplane: Signature verification TOCTOU allows installing unverified package content via mutable tag

Critical severity GitHub Reviewed Published Jun 16, 2026 in crossplane/crossplane • Updated Jun 19, 2026

Package

gomod github.com/crossplane/crossplane (Go)

Affected versions

<= 1.21.0-rc.0

Patched versions

None
gomod github.com/crossplane/crossplane/v2 (Go)
>= 2.3.0-rc.0, <= 2.3.2
<= 2.2.2
None

Description

Summary

Crossplane allows package signature verification to be configured via the ImageConfig mechanism. When enabled, the package manager uses cosign to verify that packages are correctly signed before pulling and installing them.

When a package is installed using a tag reference (e.g., a semantic version), a malicious OCI registry could serve a correctly signed image for verification, then subsequently serve an unsigned image for installation. This is possible because Crossplane resolves the tag reference separately for each step.

This vulnerability is relevant only for users who do all three of the following:

  1. Configure signature verification for packages,
  2. Install packages using tag references rather than digests, and
  3. Install packages from registries they do not control.

Mitigation

Installing packages by image digest rather than using tags avoids this issue.

Fix

The package manager has been updated to resolve tag references once and use the resulting digest for both signature verification and image fetching. This ensures that Crossplane pulls the same content that had its signature verified. The fix has been applied to Crossplane's main branch and backported to the v2.3 and v2.2 release branches; it will be released in v2.3.3 and v2.2.3.

Credits

This issue was reported, independently, by @bugbunny-research and @tonghuaroot.

References

@adamwg adamwg published to crossplane/crossplane Jun 16, 2026
Published to the GitHub Advisory Database Jun 19, 2026
Reviewed Jun 19, 2026
Last updated Jun 19, 2026

Severity

Critical

CVSS overall score

This score calculates overall vulnerability severity from 0 to 10 and is based on the Common Vulnerability Scoring System (CVSS).
/ 10

CVSS v3 base metrics

Attack vector
Network
Attack complexity
High
Privileges required
None
User interaction
None
Scope
Changed
Confidentiality
High
Integrity
High
Availability
High

CVSS v3 base metrics

Attack vector: More severe the more the remote (logically and physically) an attacker can be in order to exploit the vulnerability.
Attack complexity: More severe for the least complex attacks.
Privileges required: More severe if no privileges are required.
User interaction: More severe when no user interaction is required.
Scope: More severe when a scope change occurs, e.g. one vulnerable component impacts resources in components beyond its security scope.
Confidentiality: More severe when loss of data confidentiality is highest, measuring the level of data access available to an unauthorized user.
Integrity: More severe when loss of data integrity is the highest, measuring the consequence of data modification possible by an unauthorized user.
Availability: More severe when the loss of impacted component availability is highest.
CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:C/C:H/I:H/A:H

EPSS score

Weaknesses

Insufficient Verification of Data Authenticity

The product does not sufficiently verify the origin or authenticity of data, in a way that causes it to accept invalid data. Learn more on MITRE.

Time-of-check Time-of-use (TOCTOU) Race Condition

The product checks the state of a resource before using that resource, but the resource's state can change between the check and the use in a way that invalidates the results of the check. Learn more on MITRE.

CVE ID

No known CVE

GHSA ID

GHSA-wfqx-gjrf-g28r

Source code

Credits

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