# CVE-2026-25500: rack XSS — Fixed in 2.2.22 💎 💎 RubyGems Not in CISA KEV MEDIUM severity # CVE-2026-25500 — rack MEDIUM [Fix: rack/rack@f2f225f](https://github.com/rack/rack/commit/f2f225f297b99fbee3d9f51255d41f601fc40aff) CVE-2026-25500 is a medium-severity (CVSS 5.4) Cross-site Scripting (XSS) vulnerability in rack. A fix is available for rack — see the affected versions and patch details below. Rack's Stored XSS in Rack::Directory via javascript: filenames rendered into anchor href Also known as[GHSA-whrj-4476-wvmp](/vulnerability/GHSA-whrj-4476-wvmp) Published Feb 18, 2026 Updated Nov 11, 2026 Affected 3 pkgs Patched 3 / 3 Exploits None indexed Exploitation data as of Nov 10, 2026 · OSV.dev, NVD, FIRST.org (EPSS) ## Exploitation Status ### No confirmed exploitation observed yet - CISA’s own triage has not observed active exploitation or public proof-of-concept code for this CVE as of its last assessment. Exploitation and automatability from CISA’s SSVC triage for CVE-2026-25500. ## EPSS Exploitation Probability [via FIRST.org ↗](https://www.first.org/epss/) 0.3%probability of exploitation in next 30 days Lower Risk\-0.00% Lower risk than most CVEs19th percentile — riskier than 19% of all scored CVEsHighest risk 0.00%0.26%0.52%0.77%0.0%0.3%May 26Aug 26Nov 26 Probability of exploitation in the next 30 days, from [FIRST.org EPSS](https://www.first.org/epss/). ## How urgent is this, really ## Where this sits among everything scored ## Real-World Exposure 3 pkgs affected 💎`rack`💎`rack`💎`rack` Real-time download stats are indexed for npm and PyPI packages. This vulnerability affects RubyGems packages — download data is not available via public APIs for these ecosystems. ## Description ### Summary `Rack::Directory` generates an HTML directory index where each file entry is rendered as a clickable link. If a file exists on disk whose basename begins with the `javascript:` scheme (e.g. `javascript:alert(1)`), the generated index includes an anchor whose `href` attribute is exactly `javascript:alert(1)`. Clicking this entry executes arbitrary JavaScript in the context of the hosting application. This results in a client-side XSS condition in directory listings generated by `Rack::Directory`. ### Details `Rack::Directory` renders directory entries using an HTML row template similar to: ``` %s ``` The `%s` placeholder is populated directly with the file’s basename. If the basename begins with `javascript:`, the resulting HTML contains an executable JavaScript URL: ``` javascript:alert(1) ``` Because the value is inserted directly into the `href` attribute without scheme validation or normalization, browsers interpret it as a JavaScript URI. When a user clicks the link, the JavaScript executes in the origin of the Rack application. ### Impact If `Rack::Directory` is used to expose filesystem contents over HTTP, an attacker who can create or upload files within that directory may introduce a malicious filename beginning with `javascript:`. When a user visits the directory listing and clicks the entry, arbitrary JavaScript executes in the application's origin. Exploitation requires user interaction (clicking the malicious entry). ### Mitigation - Update to a patched version of Rack in which `Rack::Directory` prefixes generated anchors with a relative path indicator (e.g. `./filename`). - Avoid exposing user-controlled directories via `Rack::Directory`. - Apply a strict Content Security Policy (CSP) to reduce impact of potential client-side execution issues. - Where feasible, restrict or sanitize uploaded filenames to disallow dangerous URI scheme prefixes. HackerOne profile: [https://hackerone.com/thesmartshadow](https://hackerone.com/thesmartshadow) GitHub account owner: Ali Firas (@thesmartshadow) ## Affected Packages 3 total 3 fixed Ecosystem Package Vulnerable range Fix 💎RubyGems `rack` all versions 2.2.22`bundle update rack --conservative` 💎RubyGems `rack` ≥ 3.0.0.beta1&&< 3.1.20 3.1.20`bundle update rack --conservative` 💎RubyGems `rack` ≥ 3.2.0&&< 3.2.5 3.2.5`bundle update rack --conservative` ## Affected Products 1 product · 3 configurations Application `rack`rack ≥ 3.2.0 && < 3.2.5 range ## Detection & mitigation playbook Open-source dependency 1. ### Detect Scan your dependency tree (package-lock.json, pnpm-lock.yaml, requirements.txt, go.sum, etc.) for rack, including transitive dependencies — a direct dependency you never call can still pull in a vulnerable version. 2. ### Fix Update rack to 2.2.22 or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms CVE-2026-25500 is resolved across your whole dependency graph. 3. ### Workarounds Escape or sanitise the affected output on the server side rather than relying on client-side filtering, and add a Content-Security-Policy that blocks inline script execution so injected markup cannot run even if it reaches the page. ## Fixing This On Your OS If you run this on a Linux distribution, patch through your package manager against the distro's own security advisory below — it tracks the exact backported fix for your release, which can ship on a different timeline (and sometimes a different severity) than the upstream project. Red HatModerate Workaround published by Red Hat > Mitigation for this issue is either not available or the currently available options do not meet the Red Hat Product Security criteria comprising ease of use and deployment, applicability to widespread installation base or stability. Source: [Red Hat security advisory for CVE-2026-25500](https://access.redhat.com/security/cve/cve-2026-25500) (CC BY 4.0) ## Frequently Asked Questions \## Summary \`Rack::Directory\` generates an HTML directory index where each file entry is rendered as a clickable link. If a file exists on disk whose basename begins with the \`javascript:\` scheme (e.g. \`javascript:alert(1)\`), the generated index includes an anchor whose \`href\` attribute is exactly \`javascript:alert(1)\`. Clicking this entry executes arbitrary JavaScript in the context of the hosting application. This results in a client-side XSS condition in directory listings generated by \`Rack::Directory\`. ## Details \`Rack::Directory\` renders directory entries using an HTML row template si O3 Security · Impact-Aware SCA ### Is CVE-2026-25500 in your dependencies? Find it across RubyGems, including transitive dependencies. [Scan my dependencies](/book-demo) [How O3 SCA works](/impact-aware-sca)