# CVE-2026-45372: cpp-httplib: HTTP header value percent-decoding in server-side `parse_header` enables CRLF injection

> Attackers can inject CRLF sequences into HTTP headers via percent-encoded values, potentially enabling response splitting or header manipulation.

- **Severity:** Critical 9.9 (`CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:C/C:L/I:H/A:L`)
- **Exploited in the wild:** Not known
- **Login needed:** Not needed
- **Attackable:** Over the internet
- **Victim action needed:** Not needed
- **Fix available:** Yes
- **Published:** 29 May 2026
- **Updated:** 1 Jun 2026
- **Also known as:** DEBIAN-CVE-2026-45372, GHSA-xjxg-64p4-vj4m, UBUNTU-CVE-2026-45372, USN-8470-1

## What is CVE-2026-45372?

CVE-2026-45372 is a critical vulnerability in yhirose cpp-httplib, published on 29 May 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 0.44.0, when cpp-httplib's server parses an incoming request, it applies percent-decoding to every header value except Location and Referer. The validity check (is_field_value) is run before decoding, so encoded %0D%0A passes the check and is then expanded to a literal \r\n byte pair inside the stored header value. This vulnerability is fixed in 0.44.0.

Weakness: CWE-93 (Improper Neutralization of CRLF Sequences), CWE-444 (Inconsistent Interpretation of HTTP Requests)

## Which versions are affected by CVE-2026-45372?

It affects 1 product.


Products: Yhirose Cpp-Httplib.

## How do I fix CVE-2026-45372?

Upgrade to a fixed version.

## Is CVE-2026-45372 being exploited?

It is not confirmed as exploited in the wild, but public exploit code for CVE-2026-45372 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-2026-46527](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)
- [CVE-2026-21428](https://insights.sbomify.com/CVE-2026-21428/): cpp-httplib has CRLF injection in http headers (high 7.7)

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-45372 and fix it if it is affected.

What it is: CVE-2026-45372 is a critical vulnerability in yhirose cpp-httplib, published on 29 May 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-2026-45372 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-2026-45372/ (Markdown: https://insights.sbomify.com/CVE-2026-45372/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-45372
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-45372
- OSV: https://osv.dev/vulnerability/CVE-2026-45372

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-45372/
Summaries are generated and may contain mistakes; the official description above is the record.