CVE-2023-46737 (published 2023-11-07T18:15Z)

Cosign is a sigstore signing tool for OCI containers. Cosign is susceptible to a denial of service by an attacker controlled registry. An attacker who controls a remote registry can return a high number of attestations and/or signatures to Cosign and cause Cosign to enter a long loop resulting in an endless data attack. The root cause is that Cosign loops through all attestations fetched from the remote registry in pkg/cosign.FetchAttestations. The attacker needs to compromise the registry or make a request to a registry they control. When doing so, the attacker must return a high number of attestations in the response to Cosign. The result will be that the attacker can cause Cosign to go into a long or infinite loop that will prevent other users from verifying their data. In Kyvernos case, an attacker whose privileges are limited to making requests to the cluster can make a request with an image reference to their own registry, trigger the infinite loop and deny other users from completing their admission requests. Alternatively, the attacker can obtain control of the registry used by an organization and return a high number of attestations instead the expected number of attestations. The issue can be mitigated rather simply by setting a limit to the limit of attestations that Cosign will loop through. The limit does not need to be high to be within the vast majority of use cases and still prevent the endless data attack. This issue has been patched in version 2.2.1 and users are advised to upgrade.

CVSS v3 base score: 5.3, MEDIUM (CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:L)

Weakness information:
cwe_id: CWE-835
cwe_name: Loop with Unreachable Exit Condition ('Infinite Loop')
description: The product contains an iteration or loop with an exit condition that cannot be reached, i.e., an infinite loop.
extended_description: If the loop can be influenced by an attacker, this weakness could allow attackers to consume excessive resources such as CPU or memory.
         

Fix information:
repo_url: https://github.com/sigstore/cosign
commit_details: repo_url: https://github.com/sigstore/cosign
author: AdamKorcz
author_date: 2023-11-07 11:59:07+00:00
msg: Merge pull request from GHSA-vfp6-jrw2-99g9

* Add limit to number of sigs and attestations

Signed-off-by: AdamKorcz <44787359+AdamKorcz@users.noreply.github.com>

* Update pkg/cosign/fetch.go

Co-authored-by: Cody Soyland <codysoyland@gmail.com>
Signed-off-by: AdamKorcz <44787359+AdamKorcz@users.noreply.github.com>

* Update error message

Signed-off-by: Hayden B <hblauzvern@google.com>

* fix compilation error

Signed-off-by: Hayden Blauzvern <hblauzvern@google.com>

* Add e2e tests

Signed-off-by: Hayden Blauzvern <hblauzvern@google.com>

---------

Signed-off-by: AdamKorcz <44787359+AdamKorcz@users.noreply.github.com>
Signed-off-by: Hayden B <hblauzvern@google.com>
Signed-off-by: Hayden Blauzvern <hblauzvern@google.com>
Co-authored-by: Cody Soyland <codysoyland@gmail.com>
Co-authored-by: Hayden B <hblauzvern@google.com>
repository: repo_url: https://github.com/sigstore/cosign
repo_name: sigstore/cosign
description: Code signing and transparency for containers and binaries
repo_language: Go
owner: sigstore
file_changes: filename: fetch.go
change_type: ModificationType.MODIFY
diff: @@ -34,6 +34,8 @@ import (
 	"golang.org/x/sync/errgroup"
 )
 
+const maxAllowedSigsOrAtts = 100
+
 type SignedPayload struct {
 	Base64Signature  string
 	Payload          []byte
@@ -84,6 +86,9 @@ func FetchSignaturesForReference(_ context.Context, ref name.Reference, opts ...
 	if len(l) == 0 {
 		return nil, fmt.Errorf("no signatures associated with %s", ref)
 	}
+	if len(l) > maxAllowedSigsOrAtts {
+		return nil, fmt.Errorf("maximum number of signatures on an image is %d, found %d", maxAllowedSigsOrAtts, len(l))
+	}
 
 	signatures := make([]SignedPayload, len(l))
 	var g errgroup.Group
@@ -145,6 +150,10 @@ func FetchAttestations(se oci.SignedEntity, predicateType string) ([]Attestation
 	if len(l) == 0 {
 		return nil, errors.New("found no attestations")
 	}
+	if len(l) > maxAllowedSigsOrAtts {
+		errMsg := fmt.Sprintf("maximum number of attestations on an image is %d, found %d", maxAllowedSigsOrAtts, len(l))
+		return nil, errors.New(errMsg)
+	}
 
 	attestations := make([]AttestationPayload, 0, len(l))
 	var attMu sync.Mutex

programming_language: Go
filename: e2e_test.go
change_type: ModificationType.MODIFY
diff: @@ -661,6 +661,88 @@ func TestAttestationReplaceCreate(t *testing.T) {
 	}
 }
 
+func TestExcessiveAttestations(t *testing.T) {
+	repo, stop := reg(t)
+	defer stop()
+	td := t.TempDir()
+
+	imgName := path.Join(repo, "cosign-attest-download-e2e")
+
+	_, _, cleanup := mkimage(t, imgName)
+	defer cleanup()
+
+	_, privKeyPath, _ := keypair(t, td)
+	ko := options.KeyOpts{KeyRef: privKeyPath, PassFunc: passFunc}
+
+	ctx := context.Background()
+
+	slsaAttestation := `{ "buildType": "x", "builder": { "id": "2" }, "recipe": {} }`
+	slsaAttestationPath := filepath.Join(td, "attestation.slsa.json")
+	if err := os.WriteFile(slsaAttestationPath, []byte(slsaAttestation), 0600); err != nil {
+		t.Fatal(err)
+	}
+
+	vulnAttestation := `
+	{
+    "invocation": {
+      "parameters": null,
+      "uri": "invocation.example.com/cosign-testing",
+      "event_id": "",
+      "builder.id": ""
+    },
+    "scanner": {
+      "uri": "fakescanner.example.com/cosign-testing",
+      "version": "",
+      "db": {
+        "uri": "",
+        "version": ""
+      },
+      "result": null
+    },
+    "metadata": {
+      "scanStartedOn": "2022-04-12T00:00:00Z",
+      "scanFinishedOn": "2022-04-12T00:10:00Z"
+    }
+}
+`
+	ref, err := name.ParseReference(imgName)
+	if err != nil {
+		t.Fatal(err)
+	}
+	regOpts := options.RegistryOptions{}
+	ociremoteOpts, err := regOpts.ClientOpts(ctx)
+	if err != nil {
+		t.Fatal(err)
+	}
+
+	for i := 0; i < 102; i++ {
+		vulnAttestationPath := filepath.Join(td, fmt.Sprintf("attestation-%d.vuln.json", i))
+		if err := os.WriteFile(vulnAttestationPath, []byte(vulnAttestation), 0600); err != nil {
+			t.Fatal(err)
+		}
+
+		// Attest to create a vuln attestation
+		attestCommand := attest.AttestCommand{
+			KeyOpts:       ko,
+			PredicatePath: vulnAttestationPath,
+			PredicateType: "vuln",
+			Timeout:       30 * time.Second,
+			Replace:       false,
+		}
+		must(attestCommand.Exec(ctx, imgName), t)
+	}
+
+	attOpts := options.AttestationDownloadOptions{}
+	_, err = cosign.FetchAttestationsForReference(ctx, ref, attOpts.PredicateType, ociremoteOpts...)
+	if err == nil {
+		t.Fatalf("Expected an error, but 'err' was 'nil'")
+	}
+	expectedError := "maximum number of attestations on an image is 100, found 102"
+	if err.Error() != expectedError {
+		t.Errorf("Exted the error to be: '%s' but it was '%s'", expectedError, err.Error())
+	}
+}
+
 func TestAttestationReplace(t *testing.T) {
 	repo, stop := reg(t)
 	defer stop()
@@ -1254,6 +1336,38 @@ func TestDuplicateSign(t *testing.T) {
 	}
 }
 
+func TestExcessiveSignatures(t *testing.T) {
+	repo, stop := reg(t)
+	defer stop()
+	td := t.TempDir()
+
+	imgName := path.Join(repo, "cosign-e2e")
+
+	_, _, cleanup := mkimage(t, imgName)
+	defer cleanup()
+
+	ctx := context.Background()
+
+	for i := 0; i < 102; i++ {
+		_, privKeyPath, _ := keypair(t, td)
+
+		// Sign the image
+		ko := options.KeyOpts{KeyRef: privKeyPath, PassFunc: passFunc}
+		so := options.SignOptions{
+			Upload: true,
+		}
+		must(sign.SignCmd(ro, ko, so, []string{imgName}), t)
+	}
+	err := download.SignatureCmd(ctx, options.RegistryOptions{}, imgName)
+	if err == nil {
+		t.Fatal("Expected an error, but 'err' was 'nil'")
+	}
+	expectedErr := "maximum number of signatures on an image is 100, found 102"
+	if err.Error() != expectedErr {
+		t.Fatalf("Expected the error '%s', but got the error '%s'", expectedErr, err.Error())
+	}
+}
+
 func TestKeyURLVerify(t *testing.T) {
 	// TODO: re-enable once distroless images are being signed by the new client
 	t.Skip()

programming_language: Go