OpenRun: Redirect URL validation bypass using //host paths leads to Open Redirect (CVE-2026-55252)
### Summary The restrictions on redirect URLs in `openrun` can be bypassed by attackers, leading to open redirect attacks. ### Details In the current project, the referrer header value is used for subsequent redirects, so there is currently a validation for this redirect value. The current validation logic requires that the host and schema of the redirect URL be the same as the current website's URL, and finally, the path part is used for redirection. This check seems robust, but it can still be bypassed by attackers. <img width="1606" height="1346" alt="QQ20260602-140205-2-2" src="https://github.com/user-attachments/assets/83c549f3-38d7-444d-90f0-131d806f67ff" /> Here's the problem: Assuming the current website is `http://127.0.0.1:25222/`, if the attacker passes in a redirect URL of `http://127.0.0.1:25222//fushuling.com`, its host and schema are obviously the same as the current website, thus bypassing the verification. However, the issue lies in the final redirect URL, which is the path part of the URL, i.e., `//fushuling.com`. Browsers automatically complete the HTTP header for URLs starting with `//`, ultimately successfully bypassing the restriction and redirecting to the external address `http://fushuling.com`. This vulnerable behavior was successfully reproduced locally. Normally, specifying an external address directly will be blocked, so it will not redirect. <img width="1587" height="717" alt="QQ20260602-140756-2-3" src="https://github.com/user-attachments/assets/51430c42-bd10-401b-9c9f-27a91a0bc648" /> However, if the redirect URL is `http://127.0.0.1:25222//fushuling.com`, the existing validation logic is bypassed, and the Location header is successfully set to `//fushuling.com`. ``` POST /redirecttest/abc/frag HTTP/1.1 Host: 127.0.0.1:25222 Referer: http://127.0.0.1:25222//fushuling.com Cache-Control: max-age=0 sec-ch-ua: "Not(A:Brand";v="24", "Chromium";v="122" sec-ch-ua-mobile: ?0 sec-ch-ua-platform: "Windows" Upgrade-Insecure-Requests: 1 User-Agent: Mozilla/5.0 (Windows NT 10.0; Win64; x64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/122.0.6261.57 Safari/537.36 Accept: text/html,application/xhtml+xml,application/xml;q=0.9,image/avif,image/webp,image/apng,*/*;q=0.8,application/signed-exchange;v=b3;q=0.7 Sec-Fetch-Site: none Sec-Fetch-Mode: navigate Sec-Fetch-User: ?1 Sec-Fetch-Dest: document Accept-Encoding: gzip, deflate, br Accept-Language: zh-CN,zh;q=0.9 Connection: close Content-Type: application/x-www-form-urlencoded Content-Length: 0 ``` <img width="1536" height="729" alt="QQ20260602-140925-2-4" src="https://github.com/user-attachments/assets/31fde919-5f90-409f-8b14-af6c9c71761b" /> The user was then successfully redirected to the external address `http://fushuling.com`. <img width="1692" height="855" alt="QQ20260602-141005-2-5" src="https://github.com/user-attachments/assets/83b43ef6-52fa-4218-908b-7795394ae707" /> ### PoC ``` http://127.0.0.1:25222//fushuling.com ``` ### Impact Open Redirect
AI Analysis
Technical Summary
OpenRun's redirect URL validation attempts to restrict redirects to the same host and scheme as the current website by validating the referrer header. However, if an attacker supplies a redirect URL such as http://127.0.0.1:25222//fushuling.com, the validation passes because the host and scheme match. The final redirect uses the path component, which is //fushuling.com. Browsers interpret URLs starting with // as protocol-relative URLs, causing the redirect to an external domain (http://fushuling.com), thus bypassing the intended restrictions and resulting in an open redirect vulnerability (CWE-601). This behavior was reproducible locally and affects OpenRun versions before 0.17.7.
Potential Impact
This vulnerability allows attackers to perform open redirect attacks by bypassing URL validation. Users can be redirected to arbitrary external websites, which can facilitate phishing, social engineering, or other malicious activities. The vulnerability does not require authentication and can be triggered by crafting a specially formed redirect URL. There are no known exploits in the wild at this time.
Mitigation Recommendations
Patch status is not yet confirmed — check the vendor advisory for current remediation guidance. Until a fix is available, users should avoid relying solely on host and scheme validation for redirect URLs and implement stricter validation that properly handles URLs with protocol-relative paths (starting with //).
OpenRun: Redirect URL validation bypass using //host paths leads to Open Redirect (CVE-2026-55252)
Description
### Summary The restrictions on redirect URLs in `openrun` can be bypassed by attackers, leading to open redirect attacks. ### Details In the current project, the referrer header value is used for subsequent redirects, so there is currently a validation for this redirect value. The current validation logic requires that the host and schema of the redirect URL be the same as the current website's URL, and finally, the path part is used for redirection. This check seems robust, but it can still be bypassed by attackers. <img width="1606" height="1346" alt="QQ20260602-140205-2-2" src="https://github.com/user-attachments/assets/83c549f3-38d7-444d-90f0-131d806f67ff" /> Here's the problem: Assuming the current website is `http://127.0.0.1:25222/`, if the attacker passes in a redirect URL of `http://127.0.0.1:25222//fushuling.com`, its host and schema are obviously the same as the current website, thus bypassing the verification. However, the issue lies in the final redirect URL, which is the path part of the URL, i.e., `//fushuling.com`. Browsers automatically complete the HTTP header for URLs starting with `//`, ultimately successfully bypassing the restriction and redirecting to the external address `http://fushuling.com`. This vulnerable behavior was successfully reproduced locally. Normally, specifying an external address directly will be blocked, so it will not redirect. <img width="1587" height="717" alt="QQ20260602-140756-2-3" src="https://github.com/user-attachments/assets/51430c42-bd10-401b-9c9f-27a91a0bc648" /> However, if the redirect URL is `http://127.0.0.1:25222//fushuling.com`, the existing validation logic is bypassed, and the Location header is successfully set to `//fushuling.com`. ``` POST /redirecttest/abc/frag HTTP/1.1 Host: 127.0.0.1:25222 Referer: http://127.0.0.1:25222//fushuling.com Cache-Control: max-age=0 sec-ch-ua: "Not(A:Brand";v="24", "Chromium";v="122" sec-ch-ua-mobile: ?0 sec-ch-ua-platform: "Windows" Upgrade-Insecure-Requests: 1 User-Agent: Mozilla/5.0 (Windows NT 10.0; Win64; x64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/122.0.6261.57 Safari/537.36 Accept: text/html,application/xhtml+xml,application/xml;q=0.9,image/avif,image/webp,image/apng,*/*;q=0.8,application/signed-exchange;v=b3;q=0.7 Sec-Fetch-Site: none Sec-Fetch-Mode: navigate Sec-Fetch-User: ?1 Sec-Fetch-Dest: document Accept-Encoding: gzip, deflate, br Accept-Language: zh-CN,zh;q=0.9 Connection: close Content-Type: application/x-www-form-urlencoded Content-Length: 0 ``` <img width="1536" height="729" alt="QQ20260602-140925-2-4" src="https://github.com/user-attachments/assets/31fde919-5f90-409f-8b14-af6c9c71761b" /> The user was then successfully redirected to the external address `http://fushuling.com`. <img width="1692" height="855" alt="QQ20260602-141005-2-5" src="https://github.com/user-attachments/assets/83b43ef6-52fa-4218-908b-7795394ae707" /> ### PoC ``` http://127.0.0.1:25222//fushuling.com ``` ### Impact Open Redirect
CVSS v4.0
Affected software
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Weaknesses
AI-Powered Analysis
Machine-generated threat intelligence
Technical Analysis
OpenRun's redirect URL validation attempts to restrict redirects to the same host and scheme as the current website by validating the referrer header. However, if an attacker supplies a redirect URL such as http://127.0.0.1:25222//fushuling.com, the validation passes because the host and scheme match. The final redirect uses the path component, which is //fushuling.com. Browsers interpret URLs starting with // as protocol-relative URLs, causing the redirect to an external domain (http://fushuling.com), thus bypassing the intended restrictions and resulting in an open redirect vulnerability (CWE-601). This behavior was reproducible locally and affects OpenRun versions before 0.17.7.
Potential Impact
This vulnerability allows attackers to perform open redirect attacks by bypassing URL validation. Users can be redirected to arbitrary external websites, which can facilitate phishing, social engineering, or other malicious activities. The vulnerability does not require authentication and can be triggered by crafting a specially formed redirect URL. There are no known exploits in the wild at this time.
Mitigation Recommendations
Patch status is not yet confirmed — check the vendor advisory for current remediation guidance. Until a fix is available, users should avoid relying solely on host and scheme validation for redirect URLs and implement stricter validation that properly handles URLs with protocol-relative paths (starting with //).
Technical Details
- Gcve Source
- db.gcve.eu
- Osv Id
- GHSA-h5g6-xmh4-hc37
- Osv Schema Version
- 1.4.0
- Aliases
- ["CVE-2026-55252"]
- Ecosystems
- ["Go"]
- Database Specific Severity
- MODERATE
- Cvss Version
- 4.0
Threat ID: 6a50ba3f68715ace4357dda8
Added to database: 07/10/2026, 09:24:15 UTC
Last enriched: 07/10/2026, 09:33:29 UTC
Last updated: 07/31/2026, 14:48:51 UTC
Views: 51
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