CVE-2025-66570Public exploitNetwork attack vector

Unauthenticated authorization bypass via internal header shadowing

Published Dec 5, 2025 · Updated Dec 5, 2025

Authentication bypass in Yuji Hirose cpp-httplib before 0.27.0 allows remote attackers to access protected resources via crafted HTTP headers. read_headers inserts client-supplied REMOTE_ADDR and related names before Server::process_request appends trusted metadata, while get_header_value returns the first duplicate. Exploitation requires a server application that reads these header names for authorization, logging, or policy decisions, enabling IP spoofing, log poisoning, or access-control bypass.

CVSS severity10.0
Critical
EPSS probability0.33%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
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Summary

What happened

Authentication bypass in Yuji Hirose cpp-httplib before 0.27.0 allows remote attackers to access protected resources via crafted HTTP headers. read_headers inserts client-supplied REMOTE_ADDR and related names before Server::process_request appends trusted metadata, while get_header_value returns the first duplicate. Exploitation requires a server application that reads these header names for authorization, logging, or policy decisions, enabling IP spoofing, log poisoning, or access-control bypass.

The record

CVE
CVE-2025-66570
Published
Dec 5, 2025
Updated
Dec 5, 2025
Vendor
Yuji Hirose
Product
cpp-httplib
Classifications
CWE-290, CWE-345, CWE-807, T1190
Attack vector
network
Privileges
unauthenticated

Timeline

How it unfolded

  1. Dec 5, 2025CVE publishedPublication date reported by the CVE source.
  2. Dec 5, 2025Record 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=< 0.27.0

What conditions does exploitation require?

Attack vectornetwork
Required privilegesunauthenticated

What is affected?

Yuji Hirose · cpp-httplibversion=< 0.27.0

Published CVSS scores

10.0GitHub Security AdvisoryCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:C/C:H/I:H/A:N

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.

Daily unique IPsNo honeypot observations are available for this CVE in the selected window.

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-290Authentication Bypass by Spoofing
CWE-345Insufficient Verification of Data Authenticity
CWE-807Reliance on Untrusted Inputs in a Security Decision
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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