# CVE-2026-31870: cpp-httplib Affected by Remote Process Crash via Malformed Content-Length Response Header

> A malicious server can crash a cpp-httplib client application by sending a malformed Content-Length header, causing an unhandled exception and process termination.

- **Severity:** High 7.5 (`CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H`)
- **Exploited in the wild:** Not known
- **Login needed:** Not needed
- **Attackable:** Over the internet
- **Victim action needed:** Not needed
- **Fix available:** Yes
- **Published:** 11 Mar 2026
- **Updated:** 12 Mar 2026
- **Also known as:** DEBIAN-CVE-2026-31870, GHSA-39q5-hh6x-jpxx, UBUNTU-CVE-2026-31870

## What is CVE-2026-31870?

CVE-2026-31870 is a high-severity denial of service vulnerability in yhirose cpp-httplib, published on 11 Mar 2026. An attacker can exploit it over the internet without logging in, with no action from the victim.

### Official description

cpp-httplib is a C++11 single-file header-only cross platform HTTP/HTTPS library. Prior to 0.37.1, when a cpp-httplib client uses the streaming API (httplib::stream::Get, httplib::stream::Post, etc.), the library calls std::stoull() directly on the Content-Length header value received from the server with no input validation and no exception handling. std::stoull throws std::invalid_argument for non-numeric strings and std::out_of_range for values exceeding ULLONG_MAX. Since nothing catches these exceptions, the C++ runtime calls std::terminate(), which kills the process with SIGABRT. Any server the client connects to — including servers reached via HTTP redirects, third-party APIs, or man-in-the-middle positions can crash the client application with a single HTTP response. No authentication is required. No interaction from the end user is required. The crash is deterministic and immediate. This vulnerability is fixed in 0.37.1.

Weakness: CWE-248 (Uncaught Exception)

## Which versions are affected by CVE-2026-31870?

It affects 1 product.


Products: Yhirose Cpp-Httplib.

## How do I fix CVE-2026-31870?

Upgrade to a fixed version.

## Is CVE-2026-31870 being exploited?

It is not confirmed as exploited in the wild, but public exploit code for CVE-2026-31870 exists.

## Other vulnerabilities in yhirose cpp-httplib

- [CVE-2025-66570](https://insights.sbomify.com/CVE-2025-66570/): cpp-httplib Untrusted HTTP Header Handling: Internal Header Shadowing (REMOTE*/LOCAL*) (critical 10.0)
- [CVE-2026-45372](https://insights.sbomify.com/CVE-2026-45372/): cpp-httplib: HTTP header value percent-decoding in server-side `parse_header` enables CRLF injection (critical 9.9)
- [CVE-2026-46527](https://insights.sbomify.com/CVE-2026-46527/): Null dereference in cpp-httplib (high 8.7)
- [CVE-2026-32627](https://insights.sbomify.com/CVE-2026-32627/): cpp-httplib has a Silent TLS Certificate Verification Bypass on HTTPS Redirect via Proxy (high 8.7)
- [CVE-2026-22776](https://insights.sbomify.com/CVE-2026-22776/): cpp-httplib vulnerable to a denial of service (DOS) using a zip bomb (high 8.7)

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-31870 and fix it if it is affected.

What it is: CVE-2026-31870 is a high-severity denial of service vulnerability in yhirose cpp-httplib, published on 11 Mar 2026. An attacker can exploit it over the internet without logging in, with no action from the victim.
Exploitation: It is not confirmed as exploited in the wild, but public exploit code for CVE-2026-31870 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-2026-31870/ (Markdown: https://insights.sbomify.com/CVE-2026-31870/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-31870
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-31870
- OSV: https://osv.dev/vulnerability/CVE-2026-31870

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From sbomify Insights: https://insights.sbomify.com/CVE-2026-31870/
Summaries are generated and may contain mistakes; the official description above is the record.