Medium, CVSS 6.9PyPIAmendedPublished
Ciphertext Malleability Issue in Tink Java
CVE-2020-8929 · GHSA-g5vf-v6wf-7w2r
- Affected
- PyPI tink < 1.5.0
- Fixed in
- 1.5.0· Vendor fix available
- Issue
- Impact Tink's Java version before 1.5 under some circumstances allowed attackers to change the key ID part of the ciphertext, resulting in the attacker creating a second ciphertext that will decrypt to the same plaintext. This can be a problem in particular in the case of encrypting with a deterministic AEAD with a single key, and relying on the fact that there is only a single valid ciphertext per plaintext. No loss of confidentiality or loss of plaintext integrity occurs due to this problem, only ciphertext integrity is compromised. Patches The issue was fixed in this pull request. Workarounds The only workaround is to backport the fixing pull request. Details Tink uses the first five bytes of a ciphertext for a version byte and a four byte key ID. Since each key has a well defined prefix, this extends non-malleability properties (but technically not indistinguishability). However, in the Java version this prefix lookup used a hash map indexed by unicode strings instead of the byte…
Recommended action: Upgrade to 1.5.0 or later, then redeploy and verify.A vendor fix does not resolve your finding until you verify it in your own systems.