GHSA-95pr-fxf5-86gv

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Source
https://github.com/advisories/GHSA-95pr-fxf5-86gv
Import Source
https://github.com/github/advisory-database/blob/main/advisories/github-reviewed/2024/04/GHSA-95pr-fxf5-86gv/GHSA-95pr-fxf5-86gv.json
JSON Data
https://api.osv.dev/v1/vulns/GHSA-95pr-fxf5-86gv
Aliases
Related
Published
2024-04-11T17:15:46Z
Modified
2024-06-05T16:43:25.758524Z
Severity
  • 4.2 (Medium) CVSS_V3 - CVSS:3.1/AV:N/AC:H/PR:H/UI:R/S:U/C:N/I:N/A:H CVSS Calculator
Summary
Cosign malicious artifacts can cause machine-wide DoS
Details

Maliciously-crafted software artifacts can cause denial of service of the machine running Cosign, thereby impacting all services on the machine. The root cause is that Cosign creates slices based on the number of signatures, manifests or attestations in untrusted artifacts. As such, the untrusted artifact can control the amount of memory that Cosign allocates.

As an example, these lines demonstrate the problem:

https://github.com/sigstore/cosign/blob/286a98a4a99c1b2f32f84b0d560e324100312280/pkg/oci/remote/signatures.go#L56-L70

This Get() method gets the manifest of the image, allocates a slice equal to the length of the layers in the manifest, loops through the layers and adds a new signature to the slice.

The exact issue is Cosign allocates excessive memory on the lines that creates a slice of the same length as the manifests.

Remediation

Update to the latest version of Cosign, where the number of attestations, signatures and manifests has been limited to a reasonable value.

Cosign PoC

In the case of this API (also referenced above):

https://github.com/sigstore/cosign/blob/286a98a4a99c1b2f32f84b0d560e324100312280/pkg/oci/remote/signatures.go#L56-L70

… The first line can contain a length that is safe for the system and will not throw a runtime panic or be blocked by other safety mechanisms. For the sake of argument, let’s say that the length of m, err := s.Manifest() is the max allowed (by the machine without throwing OOM panics) manifests minus 1. When Cosign then allocates a new slice on this line: signatures := make([]oci.Signature, 0, len(m.Layers)), Cosign will allocate more memory than is available and the machine will be denied of service, causing Cosign and all other services on the machine to be unavailable.

To illustrate the issue here, we run a modified version of TestSignedImageIndex() in pkg/oci/remote:

https://github.com/sigstore/cosign/blob/14795db16417579fac0c00c11e166868d7976b61/pkg/oci/remote/index_test.go#L31-L57

Here, wantLayers is the number of manifests from these lines:

https://github.com/sigstore/cosign/blob/286a98a4a99c1b2f32f84b0d560e324100312280/pkg/oci/remote/signatures.go#L56-L60

To test this, we want to make wantLayers high enough to not cause a memory on its own but still trigger the machine-wide OOM when a slice gets create with the same length. On my local machine, it would take hours to create a slice of layers that fulfils that criteria, so instead I modify the Cosign production code to reflect a long list of manifests:

// Get implements oci.Signatures
func (s *sigs) Get() ([]oci.Signature, error) {
        m, err := s.Manifest()
        if err != nil {
                return nil, err
        }
        // Here we imitate a long list of manifests
        ms := make([]byte, 2600000000) // imitate a long list of manifests
        signatures := make([]oci.Signature, 0, len(ms))
        panic("Done")
        //signatures := make([]oci.Signature, 0, len(m.Layers))
        for _, desc := range m.Layers {

With this modified code, if we can cause an OOM without triggering the panic("Done"), we have succeeded.

References

Affected packages

Go / github.com/sigstore/cosign

Package

Name
github.com/sigstore/cosign
View open source insights on deps.dev
Purl
pkg:golang/github.com/sigstore/cosign

Affected ranges

Type
SEMVER
Events
Introduced
0Unknown introduced version / All previous versions are affected
Last affected
2.2.3

Go / github.com/sigstore/cosign/v2

Package

Name
github.com/sigstore/cosign/v2
View open source insights on deps.dev
Purl
pkg:golang/github.com/sigstore/cosign/v2

Affected ranges

Type
SEMVER
Events
Introduced
0Unknown introduced version / All previous versions are affected
Fixed
2.2.4

Database specific

{
    "last_known_affected_version_range": "<= 2.2.3"
}