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Fencer Vulns
medium 5.3

CVE-2020-8929 json

Ciphertext integrity weakness in Tink

published 2020-10-16 6 y ago modified 2026-07-08 4 mo ago also GHSA-g5vf-v6wf-7w2r , PYSEC-2020-142 , EUVD-2020-0220

cvss
5.3
version 3.1, CNA
cisa kev
Not listed
not in CISA's catalog
epss
0.5%
EPSS 0.5% chance of exploitation in 30 days, percentile 40%
public exploits
0
none known

Summary

A mis-handling of invalid unicode characters in the Java implementation of Tink versions prior to 1.5 allows an attacker to change the ID part of a ciphertext, which result in the creation of a second ciphertext that can decrypt to the same plaintext. This can be a problem with encrypting deterministic AEAD with a single key, and rely on a unique ciphertext-per-plaintext.

Patch / fix

  • maven com.google.crypto.tink:tink 1.5.0
  • pypi tink 1.5.0
  • Google LLC Tink 1.5

Exploit prediction

0.46% chance of exploitation in the next 30 days, higher than 40% of all scored CVEs (FIRST EPSS, 2026-11-08).

CVSS scores

assigned by version score vector
CNA 3.1 5.3 CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:L/A:N
NVD 3.1 5.3 CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:L/A:N
NVD 2.0 5.0 AV:N/AC:L/Au:N/C:N/I:P/A:N
GitHub 3.1 5.3 CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:L/A:N

Affected packages

ecosystem package affected fixed in
maven com.google.crypto.tink:tink
<1.5.0
1.5.0
pypi tink
<1.5.0
1.5.0

Affected products

  • Google LLC Tink

Classification

Weakness
  • CWE-176 Improper Handling of Unicode Encoding
  • CWE-327 Use of a Broken or Risky Cryptographic Algorithm

References

Sources

Fencer Vulns keeps one entry per vulnerability: the CVE id wins, then GHSA, and records that alias each other are merged, except that two CVEs always keep separate entries. The same data is available as JSON.