CVE-2026-45372: cpp-httplib Request Smuggling — Exploit

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.

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CVSS v3.1 Score

9.9

CRITICAL

CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:C/C:L/I:H/A:L

EPSS — Exploit Prediction

0.0025

Probability of exploitation

0.17%

Percentile rank

EPSS estimates the probability that this vulnerability will be exploited in the wild within the next 30 days. A higher score means more likely to be exploited.

Weakness Type (CWE)

CWE-93 CWE-93

CWE-444 CWE-444

Affected Products

Vendor	Product	Versions
yhirose	cpp-httplib	< 0.44.0

References

Advisories & Patches

https://github.com/yhirose/cpp-httplib/security/advisories/GHSA-xjxg-64p4-vj4m https://github.com/yhirose/cpp-httplib/security/advisories/GHSA-xjxg-64p4-vj4m

Exploits

https://github.com/yhirose/cpp-httplib/security/advisories/GHSA-xjxg-64p4-vj4m https://github.com/yhirose/cpp-httplib/security/advisories/GHSA-xjxg-64p4-vj4m

Frequently Asked Questions

What is CVE-2026-45372? +

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. It has a CVSS v3.1 base score of 9.9 (CRITICAL).

How severe is CVE-2026-45372? +

CVE-2026-45372 has a CVSS v3.1 score of 9.9 out of 10, rated CRITICAL. This is a critical vulnerability that should be patched immediately. The EPSS score is 0.0025, placing it in the 0th percentile for exploitation probability.

What products are affected by CVE-2026-45372? +

CVE-2026-45372 affects products from yhirose, specifically: cpp-httplib. Check the affected products table above for specific version ranges.

How do I check if I'm vulnerable to CVE-2026-45372? +

You can use Secably's free Website Scanner to check your website for known vulnerabilities. For infrastructure scanning, use the Port Scanner to identify exposed services that may be affected. Check the vendor advisories linked above for specific patch and version information.

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