VulnerabilityPublished 17 Sep 2025

CVE-2025-59341: esm.sh · Relative Path Traversal

Affects esm.shSource CVE Database V5

Public exploit available · CVSS 7.7 High.

Data as of 26 Oct 2026, 10:12 UTC

CVSS 4.0 base score

7.7High

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

EPSS: 1.6% chance of exploitation in 30 days – higher than 76% 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:H/VI:N/VA:N/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: High
Vulnerable system integrity: None
Vulnerable system availability: None
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: High: There is a total loss of confidentiality, resulting in all information within the Vulnerable System being divulged to the attacker. Alternatively, access to only some restricted information is obtained, but the disclosed information presents a direct, serious impact. For example, an attacker steals the administrator's password, or private encryption keys of a web server.
Vulnerable system integrity: None: There is no loss of integrity within the Vulnerable System.
Vulnerable system availability: None: There is no impact to availability within 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 17 Sep 2025
Detectable: evidence found.
nuclei template: esm.sh <= v136 - Local File Inclusion
Weaponised: evidence found.
CVSS exploit maturity: proof of concept public
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), CVSS vector, 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

Affected software

Product	Affected	Fixed in
esm-dev esm.sh	Affected <=136	Fixed in–

AI-suggested

European organizations should implement the following specific mitigations: 1) Immediately audit usage of esm.sh in their web development and production environments to identify affected versions (<=136). 2) Where possible, upgrade esm.sh to a patched version once available or apply vendor-provided fixes promptly. 3) If upgrading is not immediately feasible, implement strict network-level controls such as web application firewalls (WAFs) with custom rules to detect and block path traversal patterns in esm.sh URL requests. 4) Employ runtime monitoring and logging to detect anomalous requests targeting esm.sh endpoints, focusing on suspicious path traversal sequences. 5) Restrict access to esm.sh services via network segmentation or IP whitelisting to limit exposure. 6) Conduct thorough code reviews and scanning of web applications consuming esm.sh assets to ensure no sensitive data is inadvertently exposed. 7) Consider hosting critical JavaScript modules internally or via trusted CDNs with verified security postures to reduce reliance on vulnerable third-party services. 8) Educate development and security teams about the risks of path traversal vulnerabilities and the importance of input validation and sanitization. 9) Prepare incident response plans to quickly address potential exploitation attempts involving esm.sh. These measures go beyond generic advice by focusing on immediate detection, containment, and strategic reduction of dependency on vulnerable services.

Description

esm.sh is a nobuild content delivery network(CDN) for modern web development. In 136 and earlier, a Local File Inclusion (LFI) issue was identified in the esm.sh service URL handling. An attacker could craft a request that causes the server to read and return files from the host filesystem (or other unintended file sources).

Impact

For European organizations, the impact of CVE-2025-59341 can be significant, especially for those relying on esm.sh for delivering JavaScript modules or other web assets. Unauthorized file disclosure could lead to leakage of proprietary source code, API keys, credentials, or internal configuration files, undermining confidentiality and potentially enabling further attacks such as supply chain compromises or targeted intrusions. Organizations in sectors with stringent data protection requirements (e.g., finance, healthcare, government) face increased regulatory and reputational risks if sensitive data is exposed. Additionally, since esm.sh is a CDN service, exploitation could affect multiple clients simultaneously if the service is shared or multi-tenant, amplifying the impact. The vulnerability could also be leveraged by threat actors to gather intelligence on European organizations' internal environments, aiding in subsequent attack phases. The absence of authentication and user interaction requirements lowers the barrier for exploitation, increasing the threat surface. Furthermore, the potential exposure of development environments and build artifacts could disrupt software supply chains, a critical concern for European entities emphasizing secure software development practices.

CWE-23Relative Path Traversal (opens in a new tab)
Base weaknessOWASP Top 10 A01:2025: Broken Access Control (opens in a new tab)
The product uses external input to construct a pathname that should be within a restricted directory, but it does not properly neutralize sequences such as ".." that can resolve to a location that is outside of that directory.
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 · 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).
Operation · Firewall
Use an application firewall that can detect attacks against this weakness. It can be beneficial in cases in which the code cannot be fixed (because it is controlled by a third party), as an emergency prevention measure while more comprehensive software assurance measures are applied, or to provide defense in depth.
OWASP Cheat Sheets
Authorization (opens in a new tab)
OWASP ASVS 4.0.3
V12.3.1 (opens in a new tab)
Attack patterns
Relative Path Traversal (opens in a new tab)
Manipulating Web Input to File System Calls (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 17 Sep 2025, 18:02 UTC

Public exploits and detectiona Nuclei detection template

WeaknessesCWE-23

Technical details

References

Community reviews

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