{"id":"GHSA-g5vf-v6wf-7w2r","summary":"Ciphertext Malleability Issue in Tink Java","details":"### Impact\nTink'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.\n\nNo loss of confidentiality or loss of plaintext integrity occurs due to this problem, only ciphertext integrity is compromised.\n\n### Patches\nThe issue was fixed in this [pull request](https://github.com/google/tink/commit/93d839a5865b9d950dffdc9d0bc99b71280a8899).\n\n### Workarounds\nThe only workaround is to backport the fixing [pull request](https://github.com/google/tink/commit/93d839a5865b9d950dffdc9d0bc99b71280a8899).\n\n### Details\nTink 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 array, which means that invalid Unicode characters would be [replaced by U+FFFD](https://en.wikipedia.org/wiki/UTF-8#Invalid_sequences_and_error_handling) by the [Java API's default behavior](https://docs.oracle.com/javase/7/docs/api/java/lang/String.html#String(byte[],%20java.nio.charset.Charset)). This means several different values for the five bytes would result in the same hash table key, which allows an attacker to exchange one invalid byte sequence for another, creating a mutated ciphertext that still decrypts (to the same plaintext).\n\n### Acknowledgements\nWe'd like to thank Peter Esbensen for finding this issue and raising it internally.\n\n### For more information\nIf you have any questions or comments about this advisory:\n* Open an issue in [Tink](https://github.com/google/tink/issues)","aliases":["CVE-2020-8929","PYSEC-2020-142"],"modified":"2026-07-08T06:00:03.145975600Z","published":"2020-10-16T00:51:24Z","database_specific":{"nvd_published_at":"2020-10-19T13:15:13Z","cwe_ids":["CWE-176","CWE-327"],"severity":"MODERATE","github_reviewed":true,"github_reviewed_at":"2020-10-16T00:49:43Z"},"references":[{"type":"WEB","url":"https://github.com/google/tink/security/advisories/GHSA-g5vf-v6wf-7w2r"},{"type":"ADVISORY","url":"https://nvd.nist.gov/vuln/detail/CVE-2020-8929"},{"type":"WEB","url":"https://github.com/google/tink/commit/93d839a5865b9d950dffdc9d0bc99b71280a8899"},{"type":"WEB","url":"https://github.com/pypa/advisory-database/tree/main/vulns/tink/PYSEC-2020-142.yaml"}],"affected":[{"package":{"name":"com.google.crypto.tink:tink","ecosystem":"Maven","purl":"pkg:maven/com.google.crypto.tink/tink"},"ranges":[{"type":"ECOSYSTEM","events":[{"introduced":"0"},{"fixed":"1.5.0"}]}],"versions":["1.0.0","1.1.0","1.1.1","1.2.0","1.2.0-rc2","1.2.0-rc3","1.2.0-rc4","1.2.1","1.2.2","1.3.0","1.3.0-rc1","1.3.0-rc2","1.3.0-rc3","1.3.0-rc4","1.4.0","1.4.0-rc1","1.4.0-rc2"],"database_specific":{"source":"https://github.com/github/advisory-database/blob/main/advisories/github-reviewed/2020/10/GHSA-g5vf-v6wf-7w2r/GHSA-g5vf-v6wf-7w2r.json"}}],"schema_version":"1.9.0","severity":[{"type":"CVSS_V3","score":"CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:L/A:N"},{"type":"CVSS_V4","score":"CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:N/VI:L/VA:N/SC:N/SI:N/SA:N"}]}