Ciphertext Malleability Issue in Tink Java

Exploitation

No confirmed exploitation recorded. Patch Next marks exploitation only from CISA KEV.

CVSS 4.0

6.9 · 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 · score source

EPSS

• CVE-2020-8929: 0.46% estimated exploitation activity in the next 30 days; percentile 40.17 (FIRST EPSS, 2026-11-03). This is a model estimate, not proof of exploitation or customer exposure.

As published by the source; long descriptions are shortened.

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…

Published by the source

19 Oct 2020, 13:15 UTC

Last modified by the source

5 Jun 2025, 16:44 UTC

Source last checked

26 Oct 2026, 16:36 UTC

1. Revision 3 · amended · 26 Oct 2026

   Amended from ghsa record GHSA-g5vf-v6wf-7w2r

2. Revision 2 · amended · 25 Oct 2026

   Reviewed OSV alias/range/CVSS4 correction; package source scopes and original publication preserved. No customer finding resolved.

3. Revision 1 · created · 24 Oct 2026

   Published from osv record PYSEC-2020-142

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# Patch Next advisory brief: CVE-2020-8929

Advisory: Ciphertext Malleability Issue in Tink Java
IDs: CVE-2020-8929, GHSA-g5vf-v6wf-7w2r
Record: https://patchnext.com/advisories/cve-2020-8929 (revision 3, source checked 26 Oct 2026, 16:36 UTC)
Inventory: none attached. This brief comes from a public page and does not say whether any deployment is affected.
Severity: Medium (CVSS 6.9)
Exploitation: no confirmed exploitation recorded. Patch Next confirms exploitation only from CISA KEV.
Vendor response: Vendor fix available; fixed versions by package: com.google.crypto.tink:tink 1.5.0; tink 1.5.0. A vendor fix does not mean a deployment is fixed.

## Affected components
- Maven com.google.crypto.tink:tink: affected < 1.5.0; fixed in 1.5.0
- PyPI tink: affected < 1.5.0; fixed in 1.5.0

## Suggested inspection (read-only)
- Maven com.google.crypto.tink:tink: check the installed version with your package manager.
- `python -m pip show tink`: prints the installed version. Run with the environment that serves production active.

## Supported action
Upgrade each affected component to a fixed version on its release line. For a transitive dependency, upgrade the parent package or add an override or constraint, then regenerate the lockfile. Redeploy every environment that ran an affected version.

## Required regression checks
- Run the test suite and a production build.
- Exercise the features that depend on com.google.crypto.tink:tink, tink.
- Repeat the inspection and confirm that only fixed versions remain installed.

## Rollback considerations
- Keep the previous lockfile and deployment artifact. Rolling back reinstates the vulnerable version, so apply any documented mitigation while you fix forward.

## Unresolved questions
- Which deployments run an affected version?
- Exploitation status can change. Check again before lowering the priority.
- Mark the work resolved only after the fixed version is verified in production.

## Sources
- Verified: https://osv.dev/vulnerability/PYSEC-2020-142 (OSV record PYSEC-2020-142 lists affected ranges: PyPI tink >=0 <1.5.0 (fixed))
- Verified: https://github.com/advisories/GHSA-g5vf-v6wf-7w2r (GitHub-reviewed advisory GHSA-g5vf-v6wf-7w2r lists affected ranges: Maven com.google.crypto.tink:tink >=0 <1.5.0)

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