# CVE-2025-15536: BYVoid OpenCC out-of-bounds write in MaxMatchSegmentation

Source: https://junglewise.ai/threats/cve-2025-15536-byvoid-opencc-out-of-bounds-write-in-maxmatchsegmentation  
Publisher: Junglewise Threat Intelligence, https://junglewise.ai/threats  
Published: 2026-01-18. Updated: 2026-09-25  
License: CC BY 4.0 with a link back

CVE-2025-15536 · Severity: low · CVSS 3.1 · Published 2026-01-18

Open Chinese Convert is a library used to convert text between Traditional and Simplified Chinese characters. A memory safety vulnerability in the text processing logic allows crafted UTF-8 input to cause a heap buffer overflow. While the reported impact is local execution only, this could affect applications that process untrusted Chinese text, leading to application crashes or potential exploitation in certain contexts.

Technologies: [opencc (npm)](https://junglewise.ai/threats/technologies/opencc). Vendors: [npm](https://junglewise.ai/threats/vendors/npm).

## Quick answers

**Is CVE-2025-15536 exploited in the wild?** No. Junglewise Threat Intelligence has no report of CVE-2025-15536 being exploited in the wild.

**How severe is CVE-2025-15536?** Low severity, with a CVSS score of 3.1, published 18 January 2026.

**Which products and versions are affected?** opencc (npm) SEMVER:introduced=0,fixed=1.2.0.

**Is there a fix for CVE-2025-15536?** Yes. opencc (npm): upgrade to 1.2.0 or later. Junglewise finds every place you run it, drafts the upgrade and applies it once you approve.

**How is CVE-2025-15536 attacked?** It is attacked with local access.

**Am I affected by CVE-2025-15536?** Check whether you run opencc (npm) at an affected version. Junglewise does that check for you around the clock: connect your code, cloud and domains, and it matches new vulnerabilities like this one against what you actually run and tells you when one reaches you.

## How to fix

- opencc (npm): upgrade to 1.2.0 or later

  ```sh
  npm install opencc@1.2.0
  ```


## Technical details

The vulnerability is a heap-based out-of-bounds write (CWE-787) in the MaxMatchSegmentation::Segment function (src/MaxMatchSegmentation.cpp, line 34). The root cause is improper boundary checking when processing truncated UTF-8 sequences. The NextCharLength() function could return a value larger than the remaining input size, causing integer underflow when subtracted from a size_t length counter, leading to out-of-bounds reads/writes. The vulnerability affects OpenCC up to version 1.1.9 and requires local code execution to trigger. A patch (commit 345c9a50ab07018f1b4439776bad78a0d40778ec) released in version 1.2.0 fixes the issue by explicitly tracking buffer boundaries and clamping matched lengths to remaining buffer size. Proof-of-concept code is publicly available.

## Affected products

- BYVoid OpenCC up to 1.1.9

## Identifiers

- CVE-2025-15536
- GHSA-5pr6-crvp-2j9f

## Timeline

- 2025-12-23: disclosed: Vulnerability reported in GitHub issue #997
- 2026-01-13: patched: Fix merged in pull request #1005
- 2026-01-18: advisory: Public advisory published as CVE-2025-15536 / GHSA-5pr6-crvp-2j9f

## References

- [https://github.com/BYVoid/OpenCC/issues/997](https://github.com/BYVoid/OpenCC/issues/997)
- [https://github.com/BYVoid/OpenCC/pull/1005](https://github.com/BYVoid/OpenCC/pull/1005)
- [https://github.com/BYVoid/OpenCC/commit/345c9a50ab07018f1b4439776bad78a0d40778ec](https://github.com/BYVoid/OpenCC/commit/345c9a50ab07018f1b4439776bad78a0d40778ec)
- [https://github.com/BYVoid/OpenCC](https://github.com/BYVoid/OpenCC)
- [https://github.com/oneafter/1222/blob/main/repro](https://github.com/oneafter/1222/blob/main/repro)
- [https://vuldb.com/?ctiid.341708](https://vuldb.com/?ctiid.341708)

## Related threats

- [OpenCC out-of-bounds read in UTF-8 processing](https://junglewise.ai/threats/opencc-out-of-bounds-read-in-utf-8-processing-3c05795f)
- [Open Chinese Convert out-of-bounds read denial of service](https://junglewise.ai/threats/cve-2018-16982-open-chinese-convert-out-of-bounds-read-denial-of-service)