VulnerabilityPublished 17 Sep 2025Updated 14 Jan 2026

CVE-2025-59342: esm.sh · Path Traversal: '../filedir

Affects esm.shSource CVE Database V5

Public exploit available (Exploit-DB) · CVSS 5.5 Medium.

Data as of 26 Oct 2026, 11:42 UTC

CVSS 4.0 base score

5.5Medium

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

EPSS: 3.0% chance of exploitation in 30 days – higher than 87% 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:L/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: None
Vulnerable system integrity: Low
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: None: There is no loss of confidentiality within the Vulnerable System.
Vulnerable system 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 to 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

t = 0 is the CVE’s publication on cve.org

Disclosed: evidence found.
CVE published 17 Sep 2025
Detectable: evidence found.
nuclei template: esm.sh <= v136 - Arbitrary File Write via Path Traversal
Weaponised: evidence found.
1 Exploit-DB entry, 90 days after disclosure
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

CVE ID reserved
by GitHub, Inc.
12 Sep 202512:36 UTC, 5 days before disclosure
CVE published
on cve.org
17 Sep 202517:59 UTC, t = 0
In Threat Radar
record ingested
17 Sep 202518:09 UTC, 10 minutes after disclosure
First Exploit-DB entry (opens in a new tab)
esm-dev 136 - Path Traversal
16 Dec 2025, 90 days after disclosure

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

Affected software

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

AI-suggested

Upgrade esm.sh to version 136.1 or later immediately to apply the official patch addressing the path traversal issue.
Implement strict input validation and sanitization on all HTTP headers, especially those used in filesystem path construction, to reject or canonicalize any '../' sequences or other traversal patterns.
Employ filesystem access controls and sandboxing to limit the directories where the application can write files, minimizing the impact of any potential traversal attempts.
Monitor server logs for suspicious X-Zone-Id header values or unusual file write activities indicative of exploitation attempts.
Conduct regular security audits and code reviews focusing on path handling and input validation in web-facing components.
Consider deploying Web Application Firewalls (WAFs) with rules to detect and block path traversal payloads targeting HTTP headers.
Educate development teams on secure coding practices related to path handling to prevent recurrence of similar vulnerabilities.

Description

esm.sh is a nobuild content delivery network(CDN) for modern web development. In 136 and earlier, a path-traversal flaw in the handling of the X-Zone-Id HTTP header allows an attacker to cause the application to write files outside the intended storage location. The header value is used to build a filesystem path but is not properly canonicalized or restricted to the application’s storage base directory. As a result, supplying ../ sequences in X-Zone-Id causes files to be written to arbitrary directories. Version 136.1 contains a patch.

Impact

For European organizations, this vulnerability could lead to unauthorized file writes on servers hosting esm.sh services, potentially compromising data integrity and availability. Attackers could overwrite or inject malicious files, leading to service disruptions, defacement, or further exploitation such as remote code execution if chained with other vulnerabilities. Since esm.sh is a CDN used in modern web development, compromised servers might serve malicious content to end users, damaging organizational reputation and trust. The lack of authentication requirement increases the risk of widespread exploitation. Organizations in sectors with high reliance on web services, such as finance, e-commerce, and government, could face operational and compliance risks if exploited. Although no exploits are currently known, the vulnerability's presence in a widely used CDN component necessitates proactive mitigation to avoid potential supply chain attacks impacting European digital infrastructure.

CWE-24Path Traversal: '../filedir' (opens in a new tab)
Variant weakness
The product uses external input to construct a pathname that should be within a restricted directory, but it does not properly neutralize "../" sequences 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).
OWASP ASVS 4.0.3
V12.3.1 (opens in a new tab)
From MITRE CWE, MITRE CAPEC and OWASP (Top 10, OpenCRE).

References

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Exploitation evidence

Timeline

What to do

Affected software

Description

AI analysisMachine-generated, updated 14 Jan 2026, 19:12 UTC

Public exploits and detection1 Exploit-DB entry, a Nuclei detection template

WeaknessesCWE-24

Technical details

References

Community reviews

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