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

CISA KEV is observed exploitation evidence. FIRST EPSS is a dated prediction of exploitation in the next 30 days. Missing scores are unknown. This collector requests predictions only for explicit CVE aliases in the public NuGet archive; Microsoft release views retain their existing prediction scope.

No collected risk observation for these identifiers. This does not establish absence of exploitation or a zero probability.

## 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. ## Note on Fixed Versions The Crossplane maintainers are *not* planning to backport the fix for this advisory to the 1.20 branch, for two reasons: 1. The advisory is relevant only when an alpha feature is enabled and configured, and has a reasonable mitigation that is already a security best practice. 2. Doing so would require a major refactor of package manager internals to match the refactor that shipped in Crossplane v2.2. Such a refactor would be an unnecessary risk given the policy that v1.20 receives only critical fixes and that this advisory affects only users of an alpha feature. ## Credits This issue was reported, independently, by @bugbunny-research and @tonghuaroot.

Source published

19 Jun 2026 20:47:55 UTC

Source modified

29 Sep 2026 21:30:09 UTC

Observed here

24 Oct 2026 13:19:41 UTC

Source terms

GitHub Advisory Database · CC-BY-4.0

Original source record · Cite this exact observation · Complete original publisher JSON

This view projects the publisher's source fields for reading; the original JSON retains additional fields and CVE enrichment containers. Attribution: osv · GitHub Advisory Database · CC-BY-4.0. Source text is retained; field grouping and change labels are provided by ChangeIntel.

CVSS_V3 · CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:C/C:H/I:H/A:H

Publisher rating · CRITICAL

Crossplane: Signature verification TOCTOU allows installing unverified package content via mutable tag in github.com/crossplane/crossplane

Source published

25 Jun 2026 22:34:38 UTC

Source modified

25 Jun 2026 23:01:29 UTC

Observed here

24 Oct 2026 13:19:41 UTC

Source terms

OSV · upstream source license applies

Original source record · Cite this exact observation · Complete original publisher JSON

This view projects the publisher's source fields for reading; the original JSON retains additional fields and CVE enrichment containers. Attribution: osv · OSV · upstream source license applies. Source text is retained; field grouping and change labels are provided by ChangeIntel.