# OSV-2020-866: UNKNOWN READ in icu_64::UCharsTrie::branchNext

> An unknown read error in the ICU library's UCharsTrie can cause a crash, potentially leading to denial of service for applications using this component.

- **Severity:** Not scored
- **Exploited in the wild:** Not known
- **Login needed:** Not needed
- **Attackable:** Not stated
- **Victim action needed:** Not needed
- **Fix available:** No
- **Published:** 14 Jul 2020

## What is OSV-2020-866?

OSV-2020-866 is a memory corruption vulnerability in icu, published on 14 Jul 2020. 

### Official description

OSS-Fuzz report: https://bugs.chromium.org/p/oss-fuzz/issues/detail?id=15671

```
Crash type: UNKNOWN READ
Crash state:
icu_64::UCharsTrie::branchNext
icu_64::UCharsTrie::nextImpl
icu_64::UCharsTrie::next
```

## Which versions are affected by OSV-2020-866?

1 open source package ship an affected version, including icu.


| Package | Ecosystem | Affected | Fixed in |
| --- | --- | --- | --- |
| `icu` | OSS-Fuzz | All versions | None |

## How do I fix OSV-2020-866?

No fix has been published for OSV-2020-866 yet. Limit exposure of the affected software until one is available.

## Is OSV-2020-866 being exploited?

There is no known exploitation of OSV-2020-866 in the wild and no public exploit code.

## Fix prompt for AI coding agents

```text
Check this codebase for OSV-2020-866 and fix it if it is affected.

What it is: OSV-2020-866 is a memory corruption vulnerability in icu, published on 14 Jul 2020. 
Exploitation: There is no known exploitation of OSV-2020-866 in the wild and no public exploit code.

Affected packages and fixed versions:
- icu (OSS-Fuzz): affected all versions; no fix listed

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/OSV-2020-866/ (Markdown: https://insights.sbomify.com/OSV-2020-866/index.md)
```

## Sources

- OSV: https://osv.dev/vulnerability/OSV-2020-866

---
From sbomify Insights: https://insights.sbomify.com/OSV-2020-866/
Summaries are generated and may contain mistakes; the official description above is the record.