CVE-2026-21428

HIGHNVD 7.57.5—
EchelonGraph scoreMEDIUM confidence

This high-severity CVE scores 7.5 under NVD CVSS v3. EPSS exploit probability: 0.4%, top 69% of all CVEs by exploit prediction. GitHub Security Advisory data not yet ingested — confidence will rise once GHSA publishes (typical lag: hours to days for open-source ecosystem CVEs; never for infrastructure-only CVEs).

Triggered by: NVD CVSS baseline
Sources: epss, nvd
Elevated
7.5EG
EchelonGraph verdictPlan a fixSerious severity, but no confirmed exploitation yet.
  • High severity, but no confirmed exploitation yet
CISA-KEV: Not listedEPSS PROB: 0%CVSS: 7.5Exploit: Elevated riskExposed: 0

No vendor fix yet — apply a workaround or compensating control (WAF / firewall / segmentation) and watch for a patch.

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 v3
7.5
EG Score
7.5(medium)
EG Risk
65(Attend)
EG Risk 65/100SSVC: Attend

EG Risk is EchelonGraph's 0–100 priority score: it fuses intrinsic severity with real-world exploitation and automatability so you can rank equal-severity CVEs and fix the most dangerous first. Higher = act sooner. Distinct from the 0–10 EG Score (severity).

How it’s computed
Severity75% × 45%
Exploitation40% × 40%
Automatability100% × 15%
Action: Remediate soon — notable exploitation risk.
EPSS PROB
0%
EPSS %ILE
35%
KEV
Not listed

Published

January 1, 2026

Last Modified

June 17, 2026

Advisory Details (3)

Auto-updated Aug 6, 2026
🔬 Proof of concept available. Patch available. Sources: github_commit, github_release, github.
github Patch Available🟡 PoC Available

CRLF injection in http headers · Advisory · yhirose/cpp-httplib · GitHub

https://github.com/yhirose/cpp-httplib/security/advisories/GHSA-wpc6-j37r-jcx7
github_release Patch Available

v0.30.0

Patch available: yhirose/cpp-httplib v0.30.0

https://github.com/yhirose/cpp-httplib/releases/tag/v0.30.0
github_commit Patch Available

commit 98048a033a53 (yhirose/cpp-httplib)

Patch available: yhirose/cpp-httplib v0.33.0 (contains commit 98048a033a53)

https://github.com/yhirose/cpp-httplib/commit/98048a033a532ff22320ce1d11789f8d5710dfcd

Affected Packages

(3 across 3 ecosystems)
Debian:12(1)
PackageVulnerable rangeFixed inDependents
cpp-httplib0.11.4+ds-1 ... 0.41.0+ds-3~bpo13+1 (27 versions)——
Debian:13(1)
PackageVulnerable rangeFixed inDependents
cpp-httplib0.18.7-1 ... 0.41.0+ds-3~bpo13+1 (9 versions)——
Debian:14(1)
PackageVulnerable rangeFixed inDependents
cpp-httplib0.18.7-1 ... 0.41.0+ds-3~bpo13+1 (7 versions)0.41.0+ds-3—

Weakness Classification(1)

MITRE Common Weakness Enumeration — the root-cause categories this CVE belongs to.

Data Freshness Timeline

(refreshed 5× in last 7d / 25× in last 30d)

Each row is a source pipeline that fetched or updated this CVE on that date, with what changed. For example, "NVD update" means NVD published or revised its analysis for this CVE; "MITRE cvelistV5" means we ingested or refreshed it from the CNA feed. Most recent first.

Showing the most recent 100 of 149 total refreshes for this CVE.

  1. 2026-09-18 19:27 UTCEPSS rescore
  2. 2026-09-16 14:07 UTCEPSS rescore
  3. 2026-09-16 05:15 UTCEPSS rescore
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  16. 2026-08-31 22:34 UTCOSV refresh
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  1. 2026-08-19 17:03 UTCEPSS rescore
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  7. 2026-08-15 00:09 UTCEG score recompute
  8. 2026-08-13 22:00 UTCEPSS rescore
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  12. 2026-08-09 22:06 UTCEG score recompute
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  33. 2026-07-23 11:19 UTCOSV refresh
  34. 2026-07-23 03:06 UTCEG score recompute
  35. 2026-07-22 14:08 UTCEPSS rescore
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  45. 2026-07-16 17:03 UTCEPSS rescore
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  60. 2026-07-07 13:46 UTCEPSS rescore
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  63. 2026-07-06 06:32 UTCOSV refresh
  64. 2026-07-06 02:23 UTCEPSS rescore
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  71. 2026-06-30 23:22 UTCEPSS rescore
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  73. 2026-06-28 14:07 UTCEPSS rescore
  74. 2026-06-28 04:56 UTCEPSS rescore
  75. 2026-06-28 04:56 UTCEPSS rescore

Frequently asked(5)

What is CVE-2026-21428?
CVE-2026-21428 is a high vulnerability published on January 1, 2026. 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…
When was CVE-2026-21428 disclosed?
CVE-2026-21428 was first published in the National Vulnerability Database on January 1, 2026, with the most recent update on June 17, 2026. EchelonGraph re-ingests CVE updates from NVD on a 2-hour cycle, so this page reflects the latest published state.
Is CVE-2026-21428 actively exploited?
CVE-2026-21428 is not currently on CISA's Known Exploited Vulnerabilities catalog. FIRST EPSS estimates a 0% probability of exploitation in the next 30 days, which ranks it in the top 64.7% of all scored CVEs.
What is the CVSS score of CVE-2026-21428?
CVE-2026-21428 has a CVSS v3 base score of 7.5 (NVD).
How do I remediate CVE-2026-21428?
Patch to the fixed version published by the affected vendor. Where vendor advisories exist for CVE-2026-21428, EchelonGraph cross-links them in the Vendor Advisories panel below — those typically contain the canonical remediation steps, fixed version numbers, and any vendor-specific mitigations.

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