CVE-2025-66577VulnerabilityPublished 5 Dec 2025

CVE-2025-66577: yhirose cpp-httplib · Log Injection

Affects yhirose cpp-httplibSource CVE Database V5

Not known to be exploited · CVSS 5.3 Medium : upgrade to 0.27.0 when convenient.

Data as of 26 Oct 2026, 06:26 UTC

CVSS 3.1 base score

5.3Medium

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

EPSS: 0.2% chance of exploitation in 30 days – higher than 19% 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:U/C:N/I:L/A:N

Attack Vector: Network
Attack Complexity: Low
Privileges Required: None
User Interaction: None
Scope: Unchanged
Confidentiality: None
Integrity: Low
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: Unchanged: An exploited vulnerability can only affect resources managed by the same security authority. In this case, the vulnerable component and the impacted component are either the same, or both are managed by the same security authority.
Confidentiality: None: There is no loss of confidentiality within the impacted component.
Integrity: Low: Modification of data is possible, but the attacker does not have control over the consequence of a modification, or the amount of modification is limited. The data modification does not have a direct, serious impact on 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 2026-10-26.

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

1. Upgrade cpp-httplib to version 0.27.0 or later immediately to apply the official fix. 2. Implement additional validation and sanitization of HTTP headers such as X-Forwarded-For and X-Real-IP at the application or proxy level to prevent spoofed IP addresses from being logged. 3. Configure logging systems to correlate client IPs with other metadata (e.g., TCP connection info) to detect inconsistencies indicative of spoofing. 4. Employ anomaly detection on logs to identify unusual patterns or impossible IP address sequences that may suggest log poisoning. 5. Harden access to logging infrastructure and restrict who can modify logging configurations to prevent tampering. 6. Conduct regular audits of logs and cross-check with network-level data to ensure log integrity. 7. For organizations using cpp-httplib in embedded or IoT devices, ensure firmware updates include the patched library version and verify update mechanisms are secure. 8. Educate security teams about the risks of log poisoning and the importance of validating client IP information.

Description

CVE-2025-66577 is a medium severity vulnerability in the cpp-httplib C++ HTTP/HTTPS library versions prior to 0.27.0. It involves improper output neutralization for logs (CWE-117), allowing attacker-controlled HTTP headers such as X-Forwarded-For or X-Real-IP to spoof client IP addresses in server logs. This can lead to log poisoning and audit evasion, potentially misleading administrators and security monitoring tools. The vulnerability does not impact confidentiality or availability but affects the integrity of log data. Exploitation requires no authentication or user interaction and can be performed remotely over the network. The issue is fixed in version 0.27.0.

Impact

For European organizations, the primary impact is on the integrity and reliability of security logs, which are essential for monitoring, incident detection, and forensic analysis. Log poisoning can allow attackers to hide their true IP addresses, complicating attribution and response efforts. This is particularly critical for sectors with strict compliance and auditing requirements such as finance, healthcare, and critical infrastructure. Organizations relying on cpp-httplib in web servers, embedded systems, or IoT devices may face increased risk of stealthy attacks or unauthorized access attempts going undetected. While the vulnerability does not directly affect system confidentiality or availability, the degradation of log trustworthiness can indirectly facilitate more severe attacks by masking attacker activities. The lack of authentication or user interaction required for exploitation means attackers can remotely and easily attempt to exploit this vulnerability, increasing the likelihood of abuse if unpatched.

CWE-117Improper Output Neutralization for Logs (opens in a new tab)
Base weaknessLikelihood of exploit: MediumOWASP Top 10 A09:2025: Security Logging & Alerting Failures (opens in a new tab)
The product constructs a log message from external input, but it does not neutralize or incorrectly neutralizes special elements when the message is written to a log file.
Implementation · Input Validation
Assume all input is malicious. Use an "accept known good" input validation strategy, i.e., use a list of acceptable inputs that strictly conform to specifications. Reject any input that does not strictly conform to specifications, or transform it into something that does.
Implementation · Output Encoding
Use and specify an output encoding that can be handled by the downstream component that is reading the output. Common encodings include ISO-8859-1, UTF-7, and UTF-8.
Implementation · Input Validation
Inputs should be decoded and canonicalized to the application's current internal representation before being validated (CWE-180). Make sure that the application does not decode the same input twice (CWE-174).
OWASP Cheat Sheets
Logging (opens in a new tab)
Content Security Policy (opens in a new tab)
Application Logging Vocabulary (opens in a new tab)
OWASP ASVS 4.0.3
V7.3.1 (opens in a new tab)
V14.4.6 (opens in a new tab)
V14.4.4 (opens in a new tab)
Attack patterns
Audit Log Manipulation (opens in a new tab)
Web Server Logs Tampering (opens in a new tab)
Log Injection-Tampering-Forging (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-117, CWE-807

Technical details

References

Community reviews

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