Summary
Forge: Prototype Pollution in forge.http cookie handling via a malicious Set-Cookie
The forge.http client stored cookies from Set-Cookie response headers in a plain object keyed by cookie name and path. A malicious server could use the cookie name __proto__ to add properties to Object.prototype, use inherited names such as constructor to add properties to Object, and send an empty cookie value to delete Object.prototype properties. Fixed in node-forge 1.4.1.
Details
client.setCookie() in lib/http.js stored a cookie with client.cookies[cookie.name][cookie.path] = cookie, creating client.cookies[cookie.name] only when !(cookie.name in client.cookies). Both values come from the server's Set-Cookie header via response.getCookies(). Because in also sees inherited properties:
- a cookie named
__proto__skipped the initialization,client.cookies['__proto__']returnedObject.prototype, and the cookie path was written as a newObject.prototypeproperty, visible on every object; - a cookie named
constructorwrote onto the globalObjectfunction the same way; - a cookie with an empty value calls
client.removeCookie(name, path), which used the sameinchecks and thendelete client.cookies[name][path], soSet-Cookie: __proto__=; path=toStringdeletedObject.prototype.toString. This path skipped the cookie's secure-flag and domain checks, so it also worked forhttp://clients.
forge.http is not loaded by require('node-forge'). It is included in the forge.all browser bundle and is used with a socket pool, for example by forge.xhr.
The fix uses own-property checks for the cookie store and ignores cookies named __proto__ or with the path __proto__.
Workarounds
Don't use forge.http or forge.xhr with servers that aren't trusted, or filter Set-Cookie headers named __proto__, constructor or other Object.prototype property names before they reach the client.
Credits
Reported by @arunmozhivarman-dtx and @Dremig.
Proof of concept
A server response for a forge.http client (http.createClient({url: 'https://...', socketPool: ...})) containing:
Set-Cookie: __proto__=evil; path=polluted
On 1.4.0, after the client processes the response, ({}).polluted is the cookie object. With Set-Cookie: __proto__=; path=toLocaleString, Object.prototype.toLocaleString is deleted (for http:// and https:// clients). On 1.4.1 these cookies are ignored and Object.prototype is unchanged.
Regression tests are in tests/security/ghsa-6wvx-3r32-xmcg.js.
Impact
Applications that use the forge.http client (directly, or through forge.xhr in the forge.all browser bundle) against a server that can be malicious are affected. The server can add properties to Object.prototype and Object for the whole JavaScript realm, which can change application logic that reads properties from plain objects, and can delete built-in Object.prototype methods, breaking the page or process. Applications that don't use forge.http are not affected.
CVE-2026-118777 has a CVSS score of 4.8 (Medium). The vector is network-reachable, no privileges required, and no user interaction. A CVSS score reflects the worst-case severity of the vulnerability, not your specific exposure. Whether this affects your application depends on whether the vulnerable code is present and reachable in your environment. A fixed version is available (1.4.1); upgrading removes the vulnerable code path.
Affected versions
Security releases
Kodem intelligence
Severity tells you how bad this could be in the worst case. It does not tell you whether you are exposed. Exploitability and impact are functions of runtime truth: whether the vulnerable code is present, reachable, and actually executes in your application. A vulnerable package can sit in your dependency tree and never run.
Kodem, an Intelligent Application Security platform, uses runtime intelligence to reveal which vulnerabilities actually execute in production, so teams prioritize the ones that genuinely matter. Kodem's runtime-powered SCA identifies whether this CVE is reachable in your applications.
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Fixed in node-forge 1.4.1. Cookies from a server can no longer add or remove properties of Object.prototype or Object.
Frequently Asked Questions
- What is CVE-2026-118777? CVE-2026-118777 is a medium-severity security vulnerability in node-forge (npm), affecting versions <= 1.4.0. It is fixed in 1.4.1.
- How severe is CVE-2026-118777? CVE-2026-118777 has a CVSS score of 4.8 (Medium). This score reflects the worst-case severity of the vulnerability, not your specific exposure. Whether it represents real risk in your environment depends on whether the vulnerable code is present and reachable.
- Which versions of node-forge are affected by CVE-2026-118777? node-forge (npm) versions <= 1.4.0 is affected.
- Is there a fix for CVE-2026-118777? Yes. CVE-2026-118777 is fixed in 1.4.1. Upgrade to this version or later.
- Is CVE-2026-118777 exploitable, and should I be worried? Whether CVE-2026-118777 is exploitable in your environment depends on whether the vulnerable code is present and reachable. A CVSS score is a worst-case rating; it does not account for your specific deployment, configuration, or usage patterns. Kodem, an Intelligent Application Security platform, uses runtime intelligence to show which vulnerabilities actually execute in production, so you can focus on the ones that represent real risk. Get a demo
- What actually determines whether CVE-2026-118777 is exploitable, and how bad it is? Exploitability and impact are not fixed properties of a CVE. They depend on runtime truth: whether the vulnerable code is present, reachable, and actually executes in your application. A high CVSS score on a dependency that never runs is not the same as real risk. Kodem, an Intelligent Application Security platform, uses runtime intelligence to reveal which vulnerabilities actually execute in production, so teams prioritize the ones that genuinely matter.
- How do I fix CVE-2026-118777? Upgrade
node-forgeto 1.4.1 or later.