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Crossplane's TOCTOU between cosign verification and image fetch in xpkg.CachedClient allows tag-based package install to bypass signature check

Type: advisorySource: OSV1 source record

## 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.

Announced Source revision 1
Original source ↗

GHSA-mf7q-r4rv-jv94

Primary source · Revision 1

Imported from structured advisory data. Source references identify upstream records or fields; verify affected versions and your deployed configuration.

Security context

Source reference: osv:GHSA-mf7q-r4rv-jv94

github.com/crossplane/crossplane-runtime/v2

Source reference: /affected/0/package/name

Affected versions
2.4.0-rc.0

Source reference: /affected/0/versions

Fixed versions
2.4.0-rc.1

Source reference: /affected/0/ranges

Prerequisites
Not stated in this record

github.com/crossplane/crossplane-runtime/v2

Source reference: /affected/1/package/name

Affected versions
Not stated in this record
Fixed versions
2.3.3

Source reference: /affected/1/ranges

Prerequisites
Not stated in this record

Structured affected-version data

Original package identities and version rules from this source.

[
  {
    "ranges": [
      {
        "type": "SEMVER",
        "events": [
          {
            "introduced": "2.4.0-rc.0"
          },
          {
            "fixed": "2.4.0-rc.1"
          }
        ]
      }
    ],
    "package": {
      "name": "github.com/crossplane/crossplane-runtime/v2",
      "purl": "pkg:golang/github.com/crossplane/crossplane-runtime/v2",
      "ecosystem": "Go"
    },
    "versions": [
      "2.4.0-rc.0"
    ],
    "database_specific": {
      "source": "https://github.com/github/advisory-database/blob/main/advisories/github-reviewed/2026/08/GHSA-mf7q-r4rv-jv94/GHSA-mf7q-r4rv-jv94.json"
    }
  },
  {
    "ranges": [
      {
        "type": "SEMVER",
        "events": [
          {
            "introduced": "2.3.0"
          },
          {
            "fixed": "2.3.3"
          }
        ]
      }
    ],
    "package": {
      "name": "github.com/crossplane/crossplane-runtime/v2",
      "purl": "pkg:golang/github.com/crossplane/crossplane-runtime/v2",
      "ecosystem": "Go"
    },
    "database_specific": {
      "source": "https://github.com/github/advisory-database/blob/main/advisories/github-reviewed/2026/08/GHSA-mf7q-r4rv-jv94/GHSA-mf7q-r4rv-jv94.json",
      "last_known_affected_version_range": "<= 2.3.2"
    }
  }
]
Related CVEs
CVE-2026-105163

Source reference: /aliases

Publisher severity

high

Source reference: /database_specific/severity

Linked CVE context

These ratings describe the referenced vulnerabilities and products. They are not a severity rating for every application using this dependency.

CVE-2026-105163 · Medium

crossplane-runtime

Event
#83863 · Revision 1
Added to Heist Feed
Publisher date
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