CVE-2026-45372Public exploitNetwork attack vector

Unauthenticated CRLF injection via post-validation percent-decoding

Published May 29, 2026 · Updated May 29, 2026

CRLF injection in cpp-httplib before 0.44.0 allows remote attackers to inject control bytes through encoded request headers. The server-side parse_header validates each field value before percent-decoding it, so %0D%0A becomes literal CRLF after validation. Unauthenticated network reachability is sufficient, but downstream impact requires application code to reflect, log, or proxy the decoded value, enabling response splitting, log injection, or request smuggling.

CVSS severity9.9
Critical
EPSS probability0.29%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
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Summary

What happened

CRLF injection in cpp-httplib before 0.44.0 allows remote attackers to inject control bytes through encoded request headers. The server-side parse_header validates each field value before percent-decoding it, so %0D%0A becomes literal CRLF after validation. Unauthenticated network reachability is sufficient, but downstream impact requires application code to reflect, log, or proxy the decoded value, enabling response splitting, log injection, or request smuggling.

The record

CVE
CVE-2026-45372
Published
May 29, 2026
Updated
May 29, 2026
Vendor
Yuji Hirose
Product
cpp-httplib
Classifications
CWE-444, CWE-93, T1190
Attack vector
network
Privileges
unauthenticated

Timeline

How it unfolded

  1. May 29, 2026CVE publishedPublication date reported by the CVE source.
  2. May 29, 2026Record updatedLatest update available in the CVE record.

Exploitability

Present is not the same as exploitable

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Is a vulnerable build present?

Compare these published version ranges with your installed build and any vendor patches.

  1. Affected versionversion=< 0.44.0

What conditions does exploitation require?

Attack vectornetwork
Required privilegesunauthenticated

What is affected?

Yuji Hirose · cpp-httplibversion=< 0.44.0

Published CVSS scores

9.9GitHub, Inc.CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:C/C:L/I:H/A:L

CVSS describes severity. EPSS estimates exploitation probability.

Attacks

What attackers are doing with it

Daily unique IPs observed by Shadowserver honeypots for known exploited vulnerabilities (KEVs). Missing observations do not establish an absence of attacks.

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No observations available

Sep 9, 2026Sep 15, 2026
Latest reporting daySep 15, 2026
Latest daily unique IPsUnavailable
Prior 30-day averageUnavailable
SourceShadowserver honeypots (KEV)
Vectornetwork
Privilegesunauthenticated
Known exploitationUnconfirmed
Public exploitPublished

Weakness, pattern, technique

CWE-444Inconsistent Interpretation of HTTP Requests ('HTTP Request/Response Smuggling')
CWE-93Improper Neutralization of CRLF Sequences ('CRLF Injection')
T1190Exploit Public-Facing Application

Public exploit references

Labels summarize the accepted research assessment. They do not indicate a test against your environment.

Technologies

Your stack

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Your stack

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