CVE-2025-5399VulnerabilityPublished 7 Jun 2025Updated 9 Jun 2025

CVE-2025-5399: curl · Infinite Loop

Affects curlSource CVE Database V5

Not known to be exploited · CVSS 7.5 High.

Data as of 26 Oct 2026, 08:30 UTC

CVSS 3.1 base score

7.5High

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

EPSS: 1.3% chance of exploitation in 30 days – higher than 71% 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 7 Jun 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 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 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

Affected software

Product	Affected	Fixed in
curl curl	Affected =8.14.0 =8.13.0	Fixed in–

AI-suggested

2) Implement network-level controls to restrict or monitor WebSocket connections to untrusted or unknown servers, reducing exposure to malicious payloads. 3) Employ application-level timeouts and watchdog mechanisms to detect and recover from unresponsive states caused by infinite loops, allowing graceful termination or restart of affected processes. 4) Conduct thorough testing of applications using libcurl for WebSocket functionality to identify potential hangs or resource exhaustion scenarios. 5) Consider deploying runtime protection tools that can detect abnormal CPU usage patterns indicative of infinite loops and trigger alerts or automated remediation. 6) Maintain an inventory of software and devices using libcurl to prioritize patching and risk assessment. 7) Engage with vendors and open-source communities to track patch releases and advisories related to this vulnerability.

Description

Due to a mistake in libcurl's WebSocket code, a malicious server can send a particularly crafted packet which makes libcurl get trapped in an endless busy-loop. There is no other way for the application to escape or exit this loop other than killing the thread/process. This might be used to DoS libcurl-using application.

Impact

For European organizations, the impact of this vulnerability can be substantial, especially for those relying on libcurl for WebSocket communications in critical infrastructure, financial services, telecommunications, and cloud services. The infinite loop can cause denial of service by consuming CPU resources indefinitely, potentially leading to application crashes or degraded service availability. This can disrupt business operations, cause downtime, and impact customer trust. Since libcurl is widely used in various open-source and commercial software stacks, the vulnerability could affect a broad range of applications, including web clients, IoT devices, and backend services. The lack of authentication or user interaction requirements means attackers can exploit this vulnerability remotely and at scale, increasing the risk of widespread service disruption. European organizations with strict uptime and availability requirements, such as those in banking and healthcare sectors, may face regulatory and compliance challenges if services are interrupted due to this vulnerability.

Summary

CVE-2025-5399 is a high-severity vulnerability affecting libcurl versions 8.13.0 and 8.14.0, specifically within its WebSocket implementation. The flaw arises from a programming error that causes libcurl to enter an infinite busy-loop when interacting with a malicious WebSocket server that sends a specially crafted packet. This infinite loop has an unreachable exit condition, meaning the affected libcurl instance cannot recover or break out of the loop without forcibly terminating the thread or process. The vulnerability is classified under CWE-835 (Loop with Unreachable Exit Condition), indicating a logic flaw that leads to denial of service (DoS) conditions. Exploitation requires no authentication or user interaction and can be triggered remotely by any attacker controlling a malicious WebSocket server. The CVSS v3.1 score of 7.5 reflects a network attack vector with low complexity, no privileges required, and no user interaction, resulting in high impact on availability but no impact on confidentiality or integrity. While no known exploits are currently in the wild, the vulnerability poses a significant risk to applications and services that embed libcurl for WebSocket communication, as they can be rendered unresponsive or crash due to resource exhaustion caused by the infinite loop.

References

Community reviews

Loading reviews…

Exploitation evidence

What to do

Affected software

Description

AI analysisMachine-generated, updated 8 Jul 2025, 12:26 UTC

WeaknessesCWE-835

Technical details

References

Community reviews

Related threats