VulnerabilityPublished 25 Feb 2026

CVE-2026-27730: esm.sh · Server-Side Request Forgery (SSRF)

Affects esm.shSource CVE Database V5

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Not known to be exploited · CVSS 8.6 High.

Data as of 30 Oct 2026, 11:52 UTC

CVSS 3.0 base score

8.6High

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

EPSS: 0.3% chance of exploitation in 30 days – higher than 32% of CVEsExploit Prediction Scoring System: the likelihood attackers will use this flaw soon.

CVSS:3.0/AV:N/AC:L/PR:N/UI:N/S:C/C:H/I:N/A:N

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

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: Changed: An exploited vulnerability can affect resources beyond the security scope managed by the security authority of the vulnerable component. In this case, the vulnerable component and the impacted component are different and managed by different security authorities.
Confidentiality: High: There is total loss of confidentiality, resulting in all resources within the impacted component being divulged to the attacker. Alternatively, access to only some restricted information is obtained, but the disclosed information presents a direct, serious impact.
Integrity: None: There is no loss of integrity within the impacted component.
Availability: None: There is no impact to availability within the impacted component.

Definitions: FIRST CVSS v3.1 specification.

Exploitation evidence

Disclosed: evidence found.
CVE published 25 Feb 2026
Detectable: no evidence on record.
No public nuclei template indexed
Weaponized: 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 30 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.
Weaponized: A Metasploit exploit module or Exploit-DB entry exists (Metasploit scanner modules do not count), 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-devesm.sh	Affected <=137	Fixed in–
GitHubesm-dev/esm.sh`pkg:github/esm-dev/esm.sh`Other threats	Affected <=137	Fixed in–

Check your own hosts for these packages with threat-finder (opens in a new tab), our free open-source scanner.

AI-suggested

Until an official patch is released, organizations should implement several practical mitigations: 1) Avoid using esm.sh versions up to 137 in production environments, or disable the /http(s) fetch route if possible. 2) Employ network-level controls such as firewall rules or egress filtering on servers running esm.sh to restrict outbound requests to trusted external IPs only, preventing internal network access via SSRF. 3) Use DNS filtering or monitoring to detect and block suspicious DNS alias domains that could be used to bypass hostname checks. 4) Monitor network traffic and logs for unusual or unexpected requests originating from esm.sh servers targeting internal IP ranges. 5) Consider isolating esm.sh usage in segmented network environments with limited access to sensitive internal services. 6) Engage with the esm-dev project or community to track patch releases and apply updates promptly once available. 7) Review internal services for exposure risk and implement authentication and authorization controls to limit damage if accessed via SSRF. These targeted mitigations go beyond generic advice by focusing on network controls, DNS monitoring, and service isolation specific to the nature of this SSRF vulnerability.

Description

esm.sh is a no-build content delivery network (CDN) for web development. Versions up to and including 137 have an SSRF vulnerability (CWE-918) in esm.sh’s `/http(s)` fetch route. The service tries to block localhost/internal targets, but the validation is based on hostname string checks and can be bypassed using DNS alias domains. This allows an external requester to make the esm.sh server fetch internal localhost services. As of time of publication, no known patched versions exist.

Impact

The SSRF vulnerability in esm.sh can have severe consequences for organizations using this CDN service. Attackers can leverage the vulnerability to access internal network resources, including metadata services, internal APIs, databases, or other sensitive endpoints that are not exposed externally. This can lead to data leakage, unauthorized information gathering, and potentially facilitate further internal network compromise. Since esm.sh is a CDN used globally by web developers, the attack surface is broad. The confidentiality impact is high as internal services may contain sensitive configuration, credentials, or proprietary data. Although the vulnerability does not directly impact integrity or availability, the information gained through SSRF can be used in chained attacks to escalate privileges or disrupt services. Organizations relying on esm.sh for production or development environments are at risk, especially if internal services are accessible from the esm.sh server network. The lack of a patch increases the urgency for mitigation. The vulnerability could be exploited by remote attackers without authentication or user interaction, increasing the likelihood of exploitation once publicized.

CWE-918Server-Side Request Forgery (opens in a new tab)
Base weaknessCWE Top 25 (2025): #22OWASP Top 10 A01:2025: Broken Access Control (opens in a new tab)
The web server receives a URL or similar request from an upstream component and retrieves the contents of this URL, but it does not sufficiently ensure that the request is being sent to the expected destination.
Implementation · Operation
If there is a known list of applications, IP, hostname, and/or domains to which the product is allowed to communicate, then use allowlists to ensure that outgoing requests are restricted to these known entities. The allowlists could be in the application code or possibly enforced by firewalls or network segmentation.
Implementation · Operation
If the product is expected to be able to connect to arbitrary IP addresses or domains, consider using a denylist that includes private network addresses, internal domain names, etc. The denylist could be in the application code or possibly enforced by firewalls or network segmentation.
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.
OWASP Cheat Sheets
Server Side Request Forgery Prevention (opens in a new tab)
Unvalidated Redirects and Forwards (opens in a new tab)
Cross Site Scripting Prevention (opens in a new tab)
DOM based XSS Prevention (opens in a new tab)
Authorization (opens in a new tab)
OWASP ASVS 4.0.3
V12.6.1 (opens in a new tab)
V5.2.6 (opens in a new tab)
Attack patterns
Server Side Request Forgery (opens in a new tab)
From MITRE CWE, MITRE CAPEC and OWASP (Top 10, OpenCRE).

References

github.com/esm-dev/esm.sh/security/advisories/GHSA-p2v6-84h2-5x4r (opens in a new tab)

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Exploitation evidence

What to do

Affected software

Description

AI analysisMachine-generated, updated 25 Feb 2026, 21:11 UTC

WeaknessesCWE-918

Technical details

References

Community reviews

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