VulnerabilityPublished 29 Jan 2026Updated 3 Feb 2026

CVE-2025-63658: monkey · Stack-based Buffer Overflow

Source CVE Database V5

Not known to be exploited · CVSS 7.5 High.

Data as of 26 Oct 2026, 12:55 UTC

CVSS 3.1 base score

7.5High

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

EPSS: 1.2% chance of exploitation in 30 days – higher than 70% of CVEsExploit Prediction Scoring System: the likelihood attackers will use this flaw soon.

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

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

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: None: There is no loss of integrity within the impacted component.
Availability: High: There is total loss of availability, resulting in the attacker being able to fully deny access to resources in the impacted component; this loss is either sustained (while the attacker continues to deliver the attack) or persistent (the condition persists even after the attack has completed). Alternatively, the attacker has the ability to deny some availability, but the loss of availability presents a direct, serious consequence to the impacted component (e.g., the attacker cannot disrupt existing connections, but can prevent new connections; the attacker can repeatedly exploit a vulnerability that, in each instance of a successful attack, leaks a only small amount of memory, but after repeated exploitation causes a service to become completely unavailable).

Definitions: FIRST CVSS v3.1 specification.

Exploitation evidence

Disclosed: evidence found.
CVE published 29 Jan 2026
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 26 Oct 2026.

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 or the CVSS exploit maturity 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

AI-suggested

Monitor official Monkey HTTP server channels for security advisories and apply patches promptly once available.
In the absence of patches, implement network-level protections such as Web Application Firewalls (WAFs) or Intrusion Prevention Systems (IPS) to detect and block malformed HTTP requests targeting the mk_http_index_lookup function.
Restrict access to Monkey HTTP server instances by limiting exposure to trusted networks and employing network segmentation to reduce attack surface.
Conduct thorough input validation and sanitization on HTTP requests at the application or proxy level to prevent malformed requests from reaching the server.
For embedded devices, coordinate with device vendors to obtain firmware updates or mitigations addressing this vulnerability.
Implement robust monitoring and alerting for unusual HTTP traffic patterns indicative of exploitation attempts.
Consider deploying rate limiting to mitigate potential DoS attack volumes.
Review and harden server configurations to disable unnecessary HTTP features or modules that could be exploited.
Maintain an inventory of all systems running Monkey HTTP server to prioritize mitigation efforts.
Prepare incident response plans specifically addressing DoS scenarios impacting embedded web servers.

Description

A stack overflow in the mk_http_index_lookup function (mk_server/mk_http.c) of monkey commit f37e984 allows attackers to cause a Denial of Service (DoS) via sending a crafted HTTP request to the server.

Impact

For European organizations, the primary impact of CVE-2025-63658 is service disruption due to Denial of Service attacks against systems running the Monkey HTTP server. This can affect embedded devices, IoT gateways, or lightweight web services that rely on Monkey for HTTP handling. Critical infrastructure sectors such as manufacturing, energy, and telecommunications that utilize embedded web servers for device management could experience outages or degraded service availability. The disruption could lead to operational downtime, loss of productivity, and potential cascading effects if the affected devices are part of larger control systems. Since the vulnerability does not compromise confidentiality or integrity, data breaches are unlikely; however, the availability impact alone can be severe in time-sensitive or safety-critical environments. The lack of authentication requirement means attackers can exploit this vulnerability remotely, increasing the attack surface. European organizations with limited patch management capabilities for embedded systems may face prolonged exposure. Additionally, denial of service attacks could be leveraged as part of multi-stage attacks or to distract incident response teams.

CWE-121Stack-based Buffer Overflow (opens in a new tab)
Variant weaknessLikelihood of exploit: HighCWE Top 25 (2025): #14
A stack-based buffer overflow condition is a condition where the buffer being overwritten is allocated on the stack (i.e., is a local variable or, rarely, a parameter to a function).
Operation · Build and Compilation · Environment Hardening
Use automatic buffer overflow detection mechanisms that are offered by certain compilers or compiler extensions. Examples include: the Microsoft Visual Studio /GS flag, Fedora/Red Hat FORTIFY_SOURCE GCC flag, StackGuard, and ProPolice, which provide various mechanisms including canary-based detection and range/index…
Architecture and Design
Use an abstraction library to abstract away risky APIs. Not a complete solution.
Implementation
Implement and perform bounds checking on input.
OWASP Cheat Sheets
XML Security (opens in a new tab)
Mass Assignment (opens in a new tab)
OWASP ASVS 4.0.3
V13.3.1 (opens in a new tab)
V5.1.4 (opens in a new tab)
V5.1.3 (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

Description

AI analysisMachine-generated, updated 6 Feb 2026, 08:32 UTC

WeaknessesCWE-121

Technical details

References

Community reviews

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