# CVE-2020-8929: Ciphertext integrity weakness in Tink

> Attackers can modify ciphertext IDs to create duplicates decrypting to the same plaintext, compromising integrity in deterministic AEAD scenarios.

- **Severity:** Medium 5.3 (`CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:L/A:N`)
- **Exploited in the wild:** Not known
- **Login needed:** Not needed
- **Attackable:** Over the internet
- **Victim action needed:** Not needed
- **Fix available:** Yes
- **Published:** 19 Oct 2020
- **Updated:** 4 Aug 2024
- **Also known as:** GHSA-g5vf-v6wf-7w2r, PYSEC-2020-142

## What is CVE-2020-8929?

CVE-2020-8929 is a medium-severity vulnerability in Google LLC Tink, published on 19 Oct 2020. An attacker can exploit it over the internet without logging in, with no action from the victim.

### Official description

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.

Weakness: CWE-176 (Improper Handling of Unicode Encoding)

## Which versions are affected by CVE-2020-8929?

3 open source packages ship an affected version, including com.google.crypto.tink:tink and tink. It affects 1 product.


| Package | Ecosystem | Affected | Fixed in |
| --- | --- | --- | --- |
| `com.google.crypto.tink:tink` | Maven | All versions | 1.5.0 |
| `com.google.crypto.tink:tink` | Maven | All versions | 1.5.0 |
| `tink` | PyPI | All versions | 1.5.0 |

Products: Google Tink Java.

## How do I fix CVE-2020-8929?

Upgrade com.google.crypto.tink:tink to 1.5.0 or later.

## Is CVE-2020-8929 being exploited?

There is no known exploitation of CVE-2020-8929 in the wild and no public exploit code.

## Other vulnerabilities in Google LLC Tink

- [CVE-2026-15432](https://insights.sbomify.com/CVE-2026-15432/): Observable Timing Discrepancy in Tink-Java and Tink-Android ChunkedMacVerification (high 8.2)

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2020-8929 and fix it if it is affected.

What it is: CVE-2020-8929 is a medium-severity vulnerability in Google LLC Tink, published on 19 Oct 2020. An attacker can exploit it over the internet without logging in, with no action from the victim.
Exploitation: There is no known exploitation of CVE-2020-8929 in the wild and no public exploit code.

Affected packages and fixed versions:
- com.google.crypto.tink:tink (Maven): affected all versions; fixed in 1.5.0
- com.google.crypto.tink:tink (Maven): affected all versions; fixed in 1.5.0
- tink (PyPI): affected all versions; fixed in 1.5.0

Task:
1. Search the dependency manifests and lockfiles (for example package.json, package-lock.json, requirements.txt, poetry.lock, uv.lock, pom.xml, build.gradle, go.mod, Cargo.lock, Gemfile.lock) and any Dockerfiles for the affected packages, including transitive dependencies.
2. If an affected version is in use, upgrade it to the fixed version for its release line with the project's package manager, so the lockfile is regenerated. Prefer the smallest upgrade that fixes it.
3. If there is no fix, or the upgrade would break the build, do not guess: explain the risk and the safest workaround instead.
4. Run the tests and summarise what changed and why.
5. If nothing in the project is affected, say so and change nothing.

Reference: https://insights.sbomify.com/CVE-2020-8929/ (Markdown: https://insights.sbomify.com/CVE-2020-8929/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2020-8929
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2020-8929
- OSV: https://osv.dev/vulnerability/CVE-2020-8929

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From sbomify Insights: https://insights.sbomify.com/CVE-2020-8929/
Summaries are generated and may contain mistakes; the official description above is the record.