# OSV-2026-595: UNKNOWN WRITE in std::__1::istreambuf_iterator<char, std::__1::char_traits<char>> std::__1::num_g

> A memory corruption vulnerability in the C++ standard library's input stream handling can cause a crash when parsing specific data.

- **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:** 20 Apr 2026

## What is OSV-2026-595?

OSV-2026-595 is a memory corruption vulnerability in libigl, published on 20 Apr 2026. 

### Official description

OSS-Fuzz report: https://bugs.chromium.org/p/oss-fuzz/issues/detail?id=504141064

```
Crash type: UNKNOWN WRITE
Crash state:
std::__1::istreambuf_iterator<char, std::__1::char_traits<char>> std::__1::num_g
std::__1::basic_istream<char, std::__1::char_traits<char>>& std::__1::__input_ar
igl::MshLoader::parse_element_field
```

## Which versions are affected by OSV-2026-595?

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


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

## How do I fix OSV-2026-595?

No fix has been published for OSV-2026-595 yet. Limit exposure of the affected software until one is available.

## Is OSV-2026-595 being exploited?

There is no known exploitation of OSV-2026-595 in the wild and no public exploit code.

## Fix prompt for AI coding agents

```text
Check this codebase for OSV-2026-595 and fix it if it is affected.

What it is: OSV-2026-595 is a memory corruption vulnerability in libigl, published on 20 Apr 2026. 
Exploitation: There is no known exploitation of OSV-2026-595 in the wild and no public exploit code.

Affected packages and fixed versions:
- libigl (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-2026-595/ (Markdown: https://insights.sbomify.com/OSV-2026-595/index.md)
```

## Sources

- OSV: https://osv.dev/vulnerability/OSV-2026-595

---
From sbomify Insights: https://insights.sbomify.com/OSV-2026-595/
Summaries are generated and may contain mistakes; the official description above is the record.