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CVE-2025-27088 — s3-proxy

Fix: oxyno-zeta/s3-proxy@c611c74

CVE-2025-27088 is a Cross-site Scripting (XSS) vulnerability in github.com/oxyno-zeta/s3-proxy/cmd/s3-proxy. A fix is available for github.com/oxyno-zeta/s3-proxy/cmd/s3-proxy — see the affected versions and patch details below.

Reflected Cross-site Scripting (XSS) in template implementation in oxyno-zeta/s3-proxy

Also known asGHSA-pp9m-qf39-hxjcGO-2025-3477
Published
Updated
Affected
1 pkg
Patched
1 / 1
Exploits
None indexed
Exploitation data as of Nov 6, 2026 · OSV.dev, NVD, FIRST.org (EPSS)

Exploitation Status

Proof-of-concept exploit code exists

  • CISA’s SSVC triage found public proof-of-concept exploit code for this CVE, though no confirmed active exploitation.

Exploitation and automatability from CISA’s SSVC triage for CVE-2025-27088.

EPSS Exploitation Probability

via FIRST.org ↗
0.5%probability of exploitation in next 30 days
Lower Risk0.00%
Lower risk than most CVEs43th percentile — riskier than 43% of all scored CVEsHighest risk
0.00%0.33%0.66%1.00%0.5%0.5%May 26Sep 26Nov 26

Probability of exploitation in the next 30 days, from FIRST.org EPSS.

Real-World Exposure

1 pkg affected
🐹github.com/oxyno-zeta/s3-proxy/cmd/s3-proxy

Real-time download stats are indexed for npm and PyPI packages. This vulnerability affects Go packages — download data is not available via public APIs for these ecosystems.

Description

Summary

A Reflected Cross-site Scripting (XSS) vulnerability enables attackers to create malicious URLs that, when visited, inject scripts into the web application. This can lead to session hijacking or phishing attacks on a trusted domain, posing a high risk to all users.

Details

Give all details on the vulnerability. Pointing to the incriminated source code is very helpful for the maintainer. It's possible to inject html elements, including scripts through the folder-list template. It seems like the .Request.URL.Path variable is not escaped.

I did some research and found it might be due to the text/template import being used in the template implementation, instead of the safer html/template.

PoC

Complete instructions, including specific configuration details, to reproduce the vulnerability. Using the default template configuration, the vulnerability can be reproduced with the following steps.

  1. Navigate to https://your-s3-proxy.com/path-not-found and confirm the page looks as follows: image

  2. Try inserting an HTML element by changing /path-not-found to /<img src="x"> and confirm the page looks as follows: image

  3. Now it should be possible to run any JavaScript by manipulating the onerror property of the img element. This should make the link look like https://your-s3-proxy.com/<img src="x" onerror="alert(1)">. Confirm that going to this URL will in fact shows an alert in the browser.

Impact

The affected template allows users to interact with the URL path provided by the Request.URL.Path variable, which is then rendered directly into the HTML without proper sanitization or escaping. This can be abused by attackers who craft a malicious URL containing injected HTML or JavaScript. When users visit such a URL, the malicious script will be executed in the user's context, leading to potential risks such as:

  • Session Hijacking: Malicious scripts could be used to steal session cookies or other sensitive information.
  • Phishing Attacks: JavaScript could be injected to trick users into submitting sensitive information, such as login credentials.

This vulnerability can be exploited by attackers who craft URLs containing malicious payloads, which would then execute in the user's browser when they access the affected page. This poses a high risk to all users who visit such URLs.

Affected Packages

1 total 1 fixed
EcosystemPackageVulnerable rangeFix
🐹Gogithub.com/oxyno-zeta/s3-proxy/cmd/s3-proxyall versions0.0.0-20250220214310-c611c741ed48go get github.com/oxyno-zeta/s3-proxy/cmd/s3-proxy@v0.0.0-20250220214310-c611c741ed48

Affected Products

1 product · 3 configurations
Application
s3-proxyoxyno-zeta
< 4.18.1
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 github.com/oxyno-zeta/s3-proxy/cmd/s3-proxy, including transitive dependencies — a direct dependency you never call can still pull in a vulnerable version.

  2. Fix

    Update github.com/oxyno-zeta/s3-proxy/cmd/s3-proxy to 0.0.0-20250220214310-c611c741ed48 or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms CVE-2025-27088 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.

Frequently Asked Questions

### Summary A Reflected Cross-site Scripting (XSS) vulnerability enables attackers to create malicious URLs that, when visited, inject scripts into the web application. This can lead to session hijacking or phishing attacks on a trusted domain, posing a high risk to all users. ### Details _Give all details on the vulnerability. Pointing to the incriminated source code is very helpful for the maintainer._ It's possible to inject html elements, including scripts through the [folder-list template](https://github.com/oxyno-zeta/s3-proxy/blob/master/templates/folder-list.tpl#L19C21-L19C38). It see
O3 Security · Impact-Aware SCA

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CVE-2025-27088: s3-proxy XSS — Fix Available