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

> Attackers can inject CRLF sequences into HTTP trailer headers to split responses or forge headers in applications using cpp-httplib.

- **Severity:** Medium 5.3 (`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`)
- **Exploited in the wild:** Not known
- **Login needed:** Not needed
- **Attackable:** Over the internet
- **Victim action needed:** A user has to click or open something
- **Fix available:** Yes
- **Published:** 27 Aug 2026
- **Updated:** 28 Aug 2026
- **Also known as:** DEBIAN-CVE-2026-77341, GHSA-2r2h-jc8w-w66c, OESA-2026-4092, OESA-2026-4093, OESA-2026-4094, UBUNTU-CVE-2026-77341

## What is CVE-2026-77341?

CVE-2026-77341 is a medium-severity vulnerability in yhirose cpp-httplib, published on 27 Aug 2026. An attacker can exploit it over the internet without logging in, and only if a user opens a file or follows a link.

### Official 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.

Weakness: CWE-93 (Improper Neutralization of CRLF Sequences), CWE-113 (Improper Neutralization of CRLF Sequences in HTTP Headers)

## Which versions are affected by CVE-2026-77341?


## How do I fix CVE-2026-77341?

Upgrade to a fixed version.

## Is CVE-2026-77341 being exploited?

It is not confirmed as exploited in the wild, but public exploit code for CVE-2026-77341 exists.

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-77341 and fix it if it is affected.

What it is: CVE-2026-77341 is a medium-severity vulnerability in yhirose cpp-httplib, published on 27 Aug 2026. An attacker can exploit it over the internet without logging in, and only if a user opens a file or follows a link.
Exploitation: It is not confirmed as exploited in the wild, but public exploit code for CVE-2026-77341 exists.

Affected product: yhirose cpp-httplib. 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-2026-77341/ (Markdown: https://insights.sbomify.com/CVE-2026-77341/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-77341
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-77341
- OSV: https://osv.dev/vulnerability/CVE-2026-77341

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From sbomify Insights: https://insights.sbomify.com/CVE-2026-77341/
Summaries are generated and may contain mistakes; the official description above is the record.