CVE-2025-66570VulnerabilityPublished 5 Dec 2025

CVE-2025-66570: yhirose cpp-httplib · Authentication Bypass by Spoofing

Affects yhirose cpp-httplibSource CVE Database V5

Not known to be exploited · CVSS 10.0 Critical : upgrade to 0.27.0 as a priority.

Data as of 25 Oct 2026, 19:02 UTC

CVSS 3.1 base score

10.0Critical

How severe the flaw is on the 0–10 CVSS scale.

EPSS: 0.3% chance of exploitation in 30 days – higher than 26% of CVEsExploit Prediction Scoring System: the likelihood attackers will use this flaw soon.
Patch: Available – fixed in 0.27.0

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

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

Bold values are the worst case: easiest to exploit or largest impact.

Attack Vector: Network: The vulnerable component is bound to the network stack and the set of possible attackers extends beyond the other options listed, up to and including the entire Internet. Such a vulnerability is often termed 'remotely exploitable' and can be thought of as an attack being exploitable at the protocol level one or more network hops away (e.g., across one or more routers).
Attack Complexity: Low: Specialized access conditions or extenuating circumstances do not exist. An attacker can expect repeatable success against the vulnerable component.
Privileges Required: None: The attacker is unauthorized prior to attack, and therefore does not require any access to settings or files to carry out an attack.
User Interaction: None: The vulnerable system can be exploited without any interaction from any user.
Scope: Changed: An exploited vulnerability can affect resources beyond the security scope managed by the security authority of the vulnerable component. In this case, the vulnerable component and the impacted component are different and managed by different security authorities.
Confidentiality: High: There is total loss of confidentiality, resulting in all resources within the impacted component being divulged to the attacker. Alternatively, access to only some restricted information is obtained, but the disclosed information presents a direct, serious impact.
Integrity: High: There is a total loss of integrity, or a complete loss of protection. For example, the attacker is able to modify any/all files protected by the impacted component. Alternatively, only some files can be modified, but malicious modification would present a direct, serious consequence to the impacted component.
Availability: None: There is no impact to availability within the impacted component.

Definitions: FIRST CVSS v3.1 specification.

Exploitation evidence

Disclosed: evidence found.
CVE published 5 Dec 2025
Detectable: no evidence on record.
No public nuclei template indexed
Weaponised: no evidence on record.
No public exploit code indexed in Metasploit or Exploit-DB
Exploited in the wildExploited: no evidence on record.
Not in CISA KEV and no source reports exploitation
Observed by OffSeq MirageSeen by Mirage: no evidence on record.
No attack traffic recorded by OffSeq Mirage sensors

A missing step is not evidence of safety. Sources: cve.org (opens in a new tab), the Metasploit, Exploit-DB and nuclei-templates index as of 2026-10-25.

Disclosed: The CVE record is public on cve.org. Its publication is t = 0.
Detectable: A public nuclei template can find exposed instances, for defenders and attackers alike.
Weaponised: Public exploit code exists in Metasploit or Exploit-DB, or CISA SSVC reports a public proof of concept.
Exploited in the wild: CISA KEV lists it, CISA SSVC rates exploitation active, or a source reports attacks.
Observed by OffSeq Mirage: OffSeq Mirage honeypot sensors recorded attack traffic for this CVE, or found exposed hosts without attack traffic.

Moments are spaced evenly, not to scale; a dashed line marks a gap of six months or more. Deltas count from t = 0. Sources that give only a date (CISA KEV, Exploit-DB, or a time of exactly 00:00Z) read “same day” rather than hours. Metasploit modules carry the flaw’s disclosure date, not their release date, and nuclei templates carry no date, so both appear above but not on the timeline.

What to do

Upgrade yhirose/cpp-httplib to 0.27.0.

Affected software

Product	Affected	Fixed in
GitHubyhirose/cpp-httplib`pkg:github/yhirose/cpp-httplib`Other threats	Affected <0.27.0	Fixed in 0.27.0

Check your own hosts for these packages with threat-finder (opens in a new tab), our free open-source scanner.

AI-suggested

European organizations should immediately identify any use of cpp-httplib versions prior to 0.27.0 in their software stacks, including embedded systems, internal tools, and third-party applications. The primary mitigation is to upgrade to cpp-httplib version 0.27.0 or later, where the vulnerability is fixed by proper header handling. If upgrading is not immediately feasible, organizations should implement strict input validation and filtering at the network perimeter or application firewall to block or sanitize suspicious HTTP headers named REMOTE_ADDR, REMOTE_PORT, LOCAL_ADDR, and LOCAL_PORT. Application-level logging and authorization code should be reviewed to ensure they do not trust client-supplied headers for critical decisions. Employing additional authentication factors beyond IP-based checks can reduce risk. Monitoring logs for anomalous header values or repeated attempts to inject spoofed headers can aid early detection. Finally, organizations should conduct security testing and code reviews to verify no other header injection or spoofing vulnerabilities exist in their HTTP handling components.

Description

CVE-2025-66570 is a critical authentication bypass vulnerability in versions of the yhirose cpp-httplib library prior to 0.27.0. The flaw allows attacker-controlled HTTP headers (REMOTE_ADDR, REMOTE_PORT, LOCAL_ADDR, LOCAL_PORT) to be injected and influence server-side metadata, logging, and authorization decisions due to header shadowing. Because the library processes client headers before adding its own internal metadata headers with the same names, downstream code that retrieves header values uses attacker-supplied data, enabling IP spoofing, log poisoning, and authorization bypass without authentication or user interaction. This vulnerability affects any server using vulnerable cpp-httplib versions and can lead to full compromise of confidentiality and integrity. The issue is fixed in version 0.27.0. European organizations using cpp-httplib in web services should urgently update to mitigate risk.

Impact

For European organizations, this vulnerability poses a significant risk to web services and applications that incorporate the vulnerable cpp-httplib library. Attackers can spoof IP addresses and ports, leading to unauthorized access if IP-based authentication or authorization is used. Log poisoning can obscure attack traces or mislead incident response efforts, complicating forensic investigations. Confidentiality is at risk as attackers may impersonate legitimate clients to access sensitive data or services. Integrity is compromised because authorization decisions based on spoofed headers can allow privilege escalation or unauthorized actions. Availability is less directly impacted but could be affected if attackers leverage the bypass to perform further attacks. Given the library's cross-platform nature and use in embedded and server applications, the scope of affected systems is broad. European organizations in sectors such as finance, healthcare, government, and critical infrastructure that rely on cpp-httplib for HTTP communications are particularly vulnerable. The vulnerability's ease of exploitation without authentication or user interaction increases the likelihood of attacks, especially in environments with exposed HTTP endpoints.

CWE-290Authentication Bypass by Spoofing (opens in a new tab)
Base weaknessOWASP Top 10 A07:2025: Authentication Failures (opens in a new tab)
This attack-focused weakness is caused by incorrectly implemented authentication schemes that are subject to spoofing attacks.
OWASP Cheat Sheets
REST Security (opens in a new tab)
JSON Web Token for Java (opens in a new tab)
OWASP Authentication (opens in a new tab)
OWASP ASVS 4.0.3
V3.5.1 (opens in a new tab)
V2.8.5 (opens in a new tab)
V2.8.4 (opens in a new tab)
Attack patterns
Creating a Rogue Certification Authority Certificate (opens in a new tab)
Web Services API Signature Forgery Leveraging Hash Function Extension Weakness (opens in a new tab)
Signature Spoof (opens in a new tab)
Signature Spoofing by Misrepresentation (opens in a new tab)
Session Credential Falsification through Prediction (opens in a new tab)
From MITRE CWE, MITRE CAPEC and OWASP (Top 10, OpenCRE).
CWE-345Insufficient Verification of Data Authenticity (opens in a new tab)
Class weaknessOWASP Top 10 A08:2025: Software or Data Integrity Failures (opens in a new tab)
The product does not sufficiently verify the origin or authenticity of data, in a way that causes it to accept invalid data.
MITRE discourages mapping vulnerabilities to this broad entry; the root cause is usually a more specific weakness.
OWASP Cheat Sheets
XML Security (opens in a new tab)
REST Security (opens in a new tab)
JSON Web Token for Java (opens in a new tab)
REST Assessment (opens in a new tab)
Cross-Site Request Forgery Prevention (opens in a new tab)
OWASP ASVS 4.0.3
V13.3.2 (opens in a new tab)
V3.5.3 (opens in a new tab)
V13.2.6 (opens in a new tab)
Attack patterns
JSON Hijacking (aka JavaScript Hijacking) (opens in a new tab)
Cache Poisoning (opens in a new tab)
DNS Cache Poisoning (opens in a new tab)
Spoofing of UDDI/ebXML Messages (opens in a new tab)
Application API Message Manipulation via Man-in-the-Middle (opens in a new tab)
From MITRE CWE, MITRE CAPEC and OWASP (Top 10, OpenCRE).
CWE-807Reliance on Untrusted Inputs in a Security Decision (opens in a new tab)
Base weaknessLikelihood of exploit: HighOWASP Top 10 A06:2025: Insecure Design (opens in a new tab)
The product uses a protection mechanism that relies on the existence or values of an input, but the input can be modified by an untrusted actor in a way that bypasses the protection mechanism.
Architecture and Design · Attack Surface Reduction
Store state information and sensitive data on the server side only.
Architecture and Design · Libraries or Frameworks
Use a vetted library or framework that does not allow this weakness to occur or provides constructs that make this weakness easier to avoid.
Architecture and Design
For any security checks that are performed on the client side, ensure that these checks are duplicated on the server side, in order to avoid CWE-602. Attackers can bypass the client-side checks by modifying values after the checks have been performed, or by changing the client to remove the client-side checks…
OWASP Cheat Sheets
Secure Design Principles (opens in a new tab)
From MITRE CWE, MITRE CAPEC and OWASP (Top 10, OpenCRE).

References

Community reviews

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Exploitation evidence

What to do

Affected software

Description

AI analysisMachine-generated, updated 12 Dec 2025, 19:16 UTC

WeaknessesCWE-290, CWE-345, CWE-807

Technical details

References

Community reviews

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