cpp-httplib: HTTP header value percent-decoding in server-side `parse_header` enables CRLF injection

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Summary

CVECVE-2026-45372
StatePUBLISHED
AssignerGitHub_M
Source PriorityCVE Program / NVD first with legacy fallback
Published2026-05-29 20:16:26 UTC
Updated2026-06-01 19:16:51 UTC
Descriptioncpp-httplib is a C++11 single-file header-only cross platform HTTP/HTTPS library. Prior to 0.44.0, when cpp-httplib's server parses an incoming request, it applies percent-decoding to every header value except Location and Referer. The validity check (is_field_value) is run before decoding, so encoded %0D%0A passes the check and is then expanded to a literal \r\n byte pair inside the stored header value. This vulnerability is fixed in 0.44.0.

Risk And Classification

Primary CVSS: v3.1 9.9 CRITICAL from [email protected]

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

EPSS: 0.000560000 probability, percentile 0.178730000 (date 2026-06-07)

Problem Types: CWE-93 | CWE-444 | CWE-93 CWE-93: Improper Neutralization of CRLF Sequences ('CRLF Injection') | CWE-444 CWE-444: Inconsistent Interpretation of HTTP Requests ('HTTP Request/Response Smuggling')

VersionSourceTypeScoreSeverityVector
3.1[email protected]Secondary9.9CRITICALCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:C/C:L/I:H/A:L
3.1CNADECLARED9.9CRITICALCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:C/C:L/I:H/A:L

CVSS v3.1 Breakdown

Attack Vector
Network
Attack Complexity
Low
Privileges Required
None
User Interaction
None
Scope
Changed
Confidentiality
Low
Integrity
High
Availability
Low

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

NVD Known Affected Configurations (CPE 2.3)

TypeVendorProductVersionUpdateEditionLanguage
Application Yhirose Cpp-httplib All All All All

Vendor Declared Affected Products

SourceVendorProductVersionPlatforms
CNA Yhirose Cpp-httplib affected < 0.44.0 Not specified

References

ReferenceSourceLinkTags
github.com/yhirose/cpp-httplib/security/advisories/GHSA-xjxg-64p4-vj4m 134c704f-9b21-4f2e-91b3-4a467353bcc0 github.com Exploit, Mitigation, Vendor Advisory
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