CVSS3
Attack Vector
LOCAL
Attack Complexity
LOW
Privileges Required
LOW
User Interaction
NONE
Scope
UNCHANGED
Confidentiality Impact
HIGH
Integrity Impact
NONE
Availability Impact
NONE
CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:N/A:N
EPSS
Percentile
16.8%
In the AES GCM implementation of decrypt_in_place_detached, the decrypted ciphertext (i.e. the correct plaintext) is exposed even if tag verification fails.
If a program using the aes-gcm
crate’s decrypt_in_place*
APIs accesses the buffer after decryption failure, it will contain a decryption of an unauthenticated input. Depending on the specific nature of the program this may enable Chosen Ciphertext Attacks (CCAs) which can cause a catastrophic breakage of the cipher including full plaintext recovery.
As seen in the implementation of decrypt_in_place_detached for AES GCM, if the tag verification fails, an error is returned. Because the decryption of the ciphertext is done in place, the plaintext contents are now exposed via buffer
.
This should ideally not be the case - as noted in page 17 of NIST’s publication Recommendation for Block Cipher Modes of Operation: Galois/Counter Mode (GCM) and GMAC:
In Step 8, the result of Step 7 is compared with the authentication tag that was received as an input: if they are identical, then the plaintext is returned; otherwise,FAIL is returned.
This is seems correctly addressed in the AES GCM SIV implementation, where the decrypted buffer is encrypted again before the error is returned - this fix is straightforward to implement in AES GCM. To ensure that these types of cases are covered during testing, it would be valuable to add test cases like 23, 24 etc from project wycheproof to ensure that when a bad tag is used, there is an error on decryption and that the plaintext value is not exposed.
To reproduce this issue, I’m using test case 23 from project wycheproof.
let key = GenericArray::from_slice(&hex!("000102030405060708090a0b0c0d0e0f"));
let nonce = GenericArray::from_slice(&hex!("505152535455565758595a5b"));
let tag = GenericArray::from_slice(&hex!("d9847dbc326a06e988c77ad3863e6083")); // bad tag
let mut ct = hex!("eb156d081ed6b6b55f4612f021d87b39");
let msg = hex!("202122232425262728292a2b2c2d2e2f");
let aad = hex!("");
let cipher = Aes128Gcm::new(&key);
let _plaintext = cipher.decrypt_in_place_detached(&nonce, &aad, &mut ct, &tag);
assert_eq!(ct, msg);
Vendor | Product | Version | CPE |
---|---|---|---|
aes-gcm_project | aes-gcm | * | cpe:2.3:a:aes-gcm_project:aes-gcm:*:*:*:*:*:rust:*:* |
docs.rs/aes-gcm/latest/src/aes_gcm/lib.rs.html#309
github.com/advisories/GHSA-423w-p2w9-r7vq
github.com/RustCrypto/AEADs/security/advisories/GHSA-423w-p2w9-r7vq
lists.fedoraproject.org/archives/list/[email protected]/message/ROBB6TBDAGEQ2WIINR34F3DPSN3FND6K
lists.fedoraproject.org/archives/list/[email protected]/message/RYQCICN6BVC6I75O3F6W4VK4J3MOYDJU
lists.fedoraproject.org/archives/list/[email protected]/message/U67ZSMNX5V3WTBYPUYF45PSFG4SF5SGF
nvd.nist.gov/vuln/detail/CVE-2023-42811