CVE-2026-31870: Yhirose Cpp-httplib vulnerability (CVSS 7.5)

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.

CVSS 3.1 breakdown

Attack vectorNetwork

Attack complexityLow

Privileges requiredNone

User interactionNone

ScopeUnchanged

ConfidentialityNone

IntegrityNone

AvailabilityHigh

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

Affected products

Yhirose Cpp-httplib< 0.37.1

Remediation

Fixed in

Yhirose Cpp-httplib≥ 0.37.1

Patch & vendor advisories

https://github.com/yhirose/cpp-httplib/security/advisories/GHSA-39q5-hh6x-jpxx

References

https://github.com/yhirose/cpp-httplib/security/advisories/GHSA-39q5-hh6x-jpxxExploitMitigationVendor Advisory

Related CVEs

Recent high-severity vulnerabilities sharing a weakness type.

Frequently asked

Is CVE-2026-31870 being actively exploited?

CVE-2026-31870 is not in the CISA KEV catalog. A public exploit reference exists, so treat it as exploitable. Its EPSS exploit probability is 0.57%.

How severe is CVE-2026-31870?

CVE-2026-31870 has a CVSS 3.1 base score of 7.5, rated high. EPSS estimates a 0.57% probability of exploitation.

Which products are affected by CVE-2026-31870?

Affected products include Yhirose Cpp-httplib.

How do I fix CVE-2026-31870?

Upgrade affected software to a fixed version, for example Yhirose Cpp-httplib 0.37.1 or later, then confirm no affected versions remain in your inventory.

How Secuno handles this

Secuno correlates vulnerabilities like CVE-2026-31870 against the real software inventory on every managed device, every day. Rather than a static severity, each match is scored in context: exploit availability, EPSS, the asset's exposure, and business criticality decide where it lands in the queue. If an affected version is present anywhere across your portfolio, it surfaces automatically with a prioritised remediation path.

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