# CVE-2021-36081: Use after free in n/a

> A use-after-free vulnerability in Tesseract OCR allows attackers to potentially execute arbitrary code or cause a denial of service via crafted input.

- **Severity:** High 7.8 (`CVSS:3.1/AV:L/AC:L/PR:N/UI:R/S:U/C:H/I:H/A:H`)
- **Exploited in the wild:** Not known
- **Login needed:** Not needed
- **Attackable:** Local or same network only
- **Victim action needed:** A user has to click or open something
- **Fix available:** Yes
- **Published:** 1 Jul 2021
- **Updated:** 4 Aug 2024
- **Also known as:** DEBIAN-CVE-2021-36081, GHSA-5x29-fwcc-jm29, UBUNTU-CVE-2021-36081

## What is CVE-2021-36081?

CVE-2021-36081 is a high-severity use after free vulnerability in n/a, published on 1 Jul 2021. It can only be exploited from the same machine or local network, and only if a user opens a file or follows a link.

### Official description

Tesseract OCR 5.0.0-alpha-20201231 has a one_ell_conflict use-after-free during a strpbrk call.

Weakness: CWE-416 (Use After Free)

## Which versions are affected by CVE-2021-36081?

It affects 1 product.


Products: Tesseract-Ocr Tesseract Ocr.

## How do I fix CVE-2021-36081?

Upgrade to a fixed version.

## Is CVE-2021-36081 being exploited?

There is no known exploitation of CVE-2021-36081 in the wild and no public exploit code.

## Other vulnerabilities in n/a

- [CVE-2026-88047](https://insights.sbomify.com/CVE-2026-88047/): Tesseract: ReadNormProtos stack buffer overflow (high 8.6)
- [CVE-2026-88048](https://insights.sbomify.com/CVE-2026-88048/): Tesseract: Heap out-of-bounds write/read in FullyConnected::Forward via layer/weight-matrix dimension mismatch (high 8.6)
- [CVE-2026-88049](https://insights.sbomify.com/CVE-2026-88049/): Tesseract: Heap out-of-bounds write in LSTM::Forward via na_/gate-matrix dimension mismatch (high 8.6)
- [CVE-2026-88051](https://insights.sbomify.com/CVE-2026-88051/): Tesseract: Heap out-of-bounds write in GenericVector<T>::read due to independent reserved/size_used_ fields (high 8.6)
- [CVE-2026-88053](https://insights.sbomify.com/CVE-2026-88053/): Tesseract: Heap out-of-bounds write in Classify::ReadIntTemplates via unvalidated counts in crafted .traineddata (high 8.6)

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2021-36081 and fix it if it is affected.

What it is: CVE-2021-36081 is a high-severity use after free vulnerability in n/a, published on 1 Jul 2021. It can only be exploited from the same machine or local network, and only if a user opens a file or follows a link.
Exploitation: There is no known exploitation of CVE-2021-36081 in the wild and no public exploit code.

Affected product: n/a. No package-level version data is available, so check the vendor advisory linked from the reference page.

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-2021-36081/ (Markdown: https://insights.sbomify.com/CVE-2021-36081/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2021-36081
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2021-36081
- OSV: https://osv.dev/vulnerability/CVE-2021-36081

---
From sbomify Insights: https://insights.sbomify.com/CVE-2021-36081/
Summaries are generated and may contain mistakes; the official description above is the record.