CVE-2025-6493VulnerabilityPublished 22 Jun 2025Updated 29 Sep 2025

CVE-2025-6493: CodeMirror · ReDoS

Affects CodeMirrorSource CVE Database V5

Not known to be exploited · CVSS 6.9 Medium.

Data as of 26 Oct 2026, 06:26 UTC

CVSS 4.0 base score

6.9Medium

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

EPSS: 0.5% chance of exploitation in 30 days – higher than 44% of CVEsExploit Prediction Scoring System: the likelihood attackers will use this flaw soon.

CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:N/VI:N/VA:L/SC:N/SI:N/SA:N/E:P

Base metrics

Attack Vector: Network
Attack Complexity: Low
Attack Requirements: None
Privileges Required: None
User Interaction: None
Vulnerable system confidentiality: None
Vulnerable system integrity: None
Vulnerable system availability: Low
Subsequent system confidentiality: None
Subsequent system integrity: None
Subsequent system availability: None

Threat metrics

Exploit Maturity: POC

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

Attack Vector: Network: The vulnerable system is bound to the network stack and the set of possible attackers extends beyond the other options listed below, 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: The attacker must take no measurable action to exploit the vulnerability. The attack requires no target-specific circumvention to exploit the vulnerability. An attacker can expect repeatable success against the vulnerable system.
Attack Requirements: None: The successful attack does not depend on the deployment and execution conditions of the vulnerable system. The attacker can expect to be able to reach the vulnerability and execute the exploit under all or most instances of the vulnerability.
Privileges Required: None: The attacker is unauthorized prior to attack, and therefore does not require any access to settings or files of the vulnerable system to carry out an attack.
User Interaction: None: The vulnerable system can be exploited without interaction from any human user, other than the attacker.
Vulnerable system confidentiality: None: There is no loss of confidentiality within the Vulnerable System.
Vulnerable system integrity: None: There is no loss of integrity within the Vulnerable System.
Vulnerable system availability: Low: Performance is reduced or there are interruptions in resource availability. Even if repeated exploitation of the vulnerability is possible, the attacker does not have the ability to completely deny service to legitimate users. The resources in the Vulnerable System are either partially available all of the time, or fully available only some of the time, but overall there is no direct, serious consequence to the Vulnerable System.
Subsequent system confidentiality: None: There is no loss of confidentiality within the Subsequent System or all confidentiality impact is constrained to the Vulnerable System.
Subsequent system integrity: None: There is no loss of integrity within the Subsequent System or all integrity impact is constrained to the Vulnerable System.
Subsequent system availability: None: There is no impact to availability within the Subsequent System or all availability impact is constrained to the Vulnerable System.
Exploit Maturity: POC: Based on threat intelligence sources each of the following must apply: · Proof-of-concept is publicly available · No knowledge of reported attempts to exploit this vulnerability · No knowledge of publicly available solutions used to simplify attempts to exploit the vulnerability

Definitions: FIRST CVSS v4.0 specification.

Exploitation evidence

Disclosed: evidence found.
CVE published 22 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 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

Affected software

Product	Affected	Fixed in
npmcodemirror`pkg:npm/codemirror`Other threats	Affected <=5.65.20	Fixed in–

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AI-suggested

European organizations should take the following specific mitigation steps: 1) Immediately identify all instances of CodeMirror in their web applications, focusing on versions up to 5.65.20, especially where Markdown Mode is enabled. 2) Upgrade all affected CodeMirror components to version 6.0 or later, as this version addresses the inefficient regular expression complexity and is actively maintained. 3) Implement input validation and sanitization on Markdown inputs to limit the complexity and length of user-submitted content, reducing the risk of triggering ReDoS conditions. 4) Deploy Web Application Firewalls (WAFs) with rules designed to detect and block suspicious patterns indicative of ReDoS attacks targeting Markdown inputs. 5) Monitor application performance metrics and CPU usage to detect anomalies that may indicate ongoing exploitation attempts. 6) Apply rate limiting on endpoints that process Markdown content to mitigate the impact of automated attacks. 7) Conduct security testing and code reviews focusing on regular expression usage in custom Markdown processing logic to identify and remediate similar inefficiencies. 8) Educate development teams about the risks of ReDoS and encourage the use of safer regular expression patterns and libraries.

Description

A weakness has been identified in CodeMirror up to 5.65.20. Affected is an unknown function of the file mode/markdown/markdown.js of the component Markdown Mode. This manipulation causes inefficient regular expression complexity. It is possible to initiate the attack remotely. The exploit has been made available to the public and could be exploited. Upgrading to version 6.0 is able to address this issue. You should upgrade the affected component. Not all code samples mentioned in the GitHub issue can be found. The repository mentions, that "CodeMirror 6 exists, and is [...] much more actively maintained."

Impact

For European organizations, the primary impact of this vulnerability is the potential for denial-of-service attacks against web applications that embed vulnerable versions of CodeMirror for Markdown editing or rendering. This could disrupt services, degrade user experience, and cause operational downtime, especially for SaaS providers, educational platforms, and collaborative tools that rely on Markdown editing features. While the vulnerability does not lead to data breaches or code execution, the availability impact can be significant, particularly for high-traffic or critical services. Organizations in sectors such as finance, healthcare, government, and media that utilize web-based content management or developer collaboration tools may face service interruptions. Additionally, the ease of remote exploitation without authentication increases the risk of opportunistic attacks. Given the public availability of exploit code, attackers could automate attacks to target vulnerable endpoints, potentially leading to widespread service degradation. The impact is compounded if organizations do not have adequate resource limits or monitoring in place to detect abnormal CPU usage patterns caused by ReDoS attacks.

Summary

CVE-2025-6493 is a vulnerability identified in CodeMirror versions up to 5.65.20, specifically within the Markdown Mode component located in the file mode/markdown/markdown.js. The issue arises from inefficient regular expression complexity, which can be exploited remotely without any authentication or user interaction. This inefficiency can lead to excessive CPU consumption when processing crafted Markdown input, effectively causing a denial-of-service (DoS) condition by exhausting system resources. The vulnerability is rooted in the way certain regular expressions are constructed and evaluated, leading to what is commonly known as a Regular Expression Denial of Service (ReDoS). The exploit does not compromise confidentiality, integrity, or availability directly beyond resource exhaustion but can disrupt service availability. The vulnerability has a CVSS 4.0 base score of 6.9, indicating a medium severity level. The attack vector is network-based, requiring no privileges or user interaction, making it relatively easy to exploit remotely. The maintainers recommend upgrading to CodeMirror version 6.0, which is more actively maintained and addresses this issue. No known exploits are currently observed in the wild, but proof-of-concept code has been made publicly available, increasing the risk of exploitation. CodeMirror is a widely used JavaScript library for code editing in web applications, often embedded in content management systems, developer tools, and collaborative platforms that support Markdown editing. Therefore, any web service using vulnerable versions of CodeMirror for Markdown rendering or editing is potentially at risk.

References

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