Is CVE-2026-21428 in the CISA KEV catalog?

No. CVE-2026-21428 is not currently on the CISA Known Exploited Vulnerabilities list.

What is the CVSS severity of CVE-2026-21428?

CVE-2026-21428 has a CVSS v3 base score of 7.5 (HIGH).

What is the EPSS score for CVE-2026-21428?

CVE-2026-21428 has an EPSS score of 0.37% (29th percentile), estimating the probability of exploitation in the next 30 days.

CVE & CISA-KEV Catalog

CVE-2026-21428

HIGH

7.5

CVSS v3

NVD

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.

CWE-93

CVSS v3 Vector

Exploitability

Attack VectorNetwork

Attack ComplexityLow

Privileges RequiredNone

User InteractionNone

ScopeUnchanged

Impact

ConfidentialityNone

IntegrityHigh

AvailabilityNone

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

Exploit Intelligence

0.37%probability of exploitation in 30 days

29thpercentile

Low risk: more likely to be exploited than 29% of all known CVEs.

References

Find and fix vulnerabilities across your fleet

TridentStack Control continuously scans your Windows, macOS, and Linux fleet for known vulnerabilities, prioritizes them by severity and active exploitation, and patches them automatically.

Start free

This product uses NVD data but is not endorsed or certified by the NVD. EPSS scores courtesy of FIRST.org (https://www.first.org/epss). Source: CISA KEV Catalog. Data as of 2026-01-06.