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CVE-2026-21428

Yhirose Cpp-httplib vulnerability

7.5 HIGHPublic exploitEPSS 0.41%
  1. Published1 Jan 2026

Description

cpp-httplib is a C++11 single-file header-only cross platform HTTP/HTTPS library. Prior to version 0.30.0, the ``write_headers`` function does not check for CR & LF characters in user supplied headers, allowing untrusted header value to escape header lines. This vulnerability allows attackers to add extra headers, modify request body unexpectedly & trigger an SSRF attack. When combined with a server that supports http1.1 pipelining (springboot, python twisted etc), this can be used for server side request forgery (SSRF). Version 0.30.0 fixes this issue.

CVSS 3.1 breakdown

Attack vectorNetwork
Attack complexityLow
Privileges requiredNone
User interactionNone
ScopeUnchanged
ConfidentialityNone
IntegrityHigh
AvailabilityNone
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:H/A:N

Affected products

Yhirose Cpp-httplib< 0.30.0

Remediation

Fixed in
Yhirose Cpp-httplib≥ 0.30.0

References

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Frequently asked

Is CVE-2026-21428 being actively exploited?

CVE-2026-21428 is not in the CISA KEV catalog. A public exploit reference exists, so treat it as exploitable. Its EPSS exploit probability is 0.41%.

How severe is CVE-2026-21428?

CVE-2026-21428 has a CVSS 3.1 base score of 7.5, rated high. EPSS estimates a 0.41% probability of exploitation.

Which products are affected by CVE-2026-21428?

Affected products include Yhirose Cpp-httplib.

How do I fix CVE-2026-21428?

Upgrade affected software to a fixed version, for example Yhirose Cpp-httplib 0.30.0 or later, then confirm no affected versions remain in your inventory.

How Secuno handles this

Secuno correlates vulnerabilities like CVE-2026-21428 against the real software inventory on every managed device, as each hourly inventory arrives. 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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Data from the NVD, CISA KEV catalog and FIRST EPSS. CVSS 3.1 base score shown where available.