CefSharp: `FolderSchemeHandlerFactory` path boundary check can expose files outside the configured root folder

CISA KEV lists vulnerabilities known to be exploited. FIRST EPSS estimates the likelihood of exploitation in the next 30 days. An unavailable score does not mean zero risk.

CefSharp provides .NET bindings for the Chromium Embedded Framework for Windows Forms and Windows Presentation Foundation applications. Prior to version 148.0.90, CefSharp/SchemeHandler/FolderSchemeHandlerFactory.cs used filePath.StartsWith(rootFolder, StringComparison.OrdinalIgnoreCase) to decide whether a decoded and canonicalized request path remained inside rootFolder. That raw prefix test did not enforce a directory boundary, so a request such as ..%2fwww2/secret.txt could escape a configured www directory into a sibling www2 directory whose path shared the same string prefix. Applications that register FolderSchemeHandlerFactory for a custom scheme or an HTTP or HTTPS scheme can therefore serve local files outside the intended root when an attacker can cause the embedded browser to request the crafted URL. The issue affects both Unix-style paths such as /tmp/app/www2 and Windows paths such as C:\app\www2, and the fix appends a directory separator to the normalized root before comparison while rejecting null bytes and alternate data stream syntax. This issue is fixed in version 148.0.90.

Source published

18 Aug 2026 21:17:16 UTC

Source modified

19 Aug 2026 18:19:59 UTC

Saved here

23 Oct 2026 15:48:27 UTC

Source terms

CVE Program Terms of Use

Original source record · Cite this exact observation · Complete original publisher JSON

Source: cve-program · CVE Program Terms of Use. The publisher's wording is preserved. ChangeIntel groups the information and labels changes. The JSON record includes additional source fields.

CVSS 3.1 · 5.3 CVSS:3.1/AV:N/AC:H/PR:N/UI:R/S:U/C:H/I:N/A:N

CefSharp provides .NET bindings for the Chromium Embedded Framework for Windows Forms and Windows Presentation Foundation applications. Prior to version 148.0.90, CefSharp/SchemeHandler/FolderSchemeHandlerFactory.cs used filePath.StartsWith(rootFolder, StringComparison.OrdinalIgnoreCase) to decide whether a decoded and canonicalized request path remained inside rootFolder. That raw prefix test did not enforce a directory boundary, so a request such as ..%2fwww2/secret.txt could escape a configured www directory into a sibling www2 directory whose path shared the same string prefix. Applications that register FolderSchemeHandlerFactory for a custom scheme or an HTTP or HTTPS scheme can therefore serve local files outside the intended root when an attacker can cause the embedded browser to request the crafted URL. The issue affects both Unix-style paths such as /tmp/app/www2 and Windows paths such as C:\app\www2, and the fix appends a directory separator to the normalized root before comparison while rejecting null bytes and alternate data stream syntax. This issue is fixed in version 148.0.90.

Source published

Aug 18, 2026, 9:17:16 PM (timezone not stated)

Source modified

Aug 19, 2026, 6:19:59 PM (timezone not stated)

Saved here

13 Nov 2026 13:59:55 UTC

Source terms

ENISA EUVD · source terms and attribution apply

Original source record · Cite this exact observation · Complete original publisher JSON

Source: euvd · ENISA EUVD · source terms and attribution apply. The publisher's wording is preserved. ChangeIntel groups the information and labels changes. The JSON record includes additional source fields.

EUVD CVSS 3.1 · 5.3 CVSS:3.1/AV:N/AC:H/PR:N/UI:R/S:U/C:H/I:N/A:N

CefSharp provides .NET bindings for the Chromium Embedded Framework for Windows Forms and Windows Presentation Foundation applications. Prior to version 148.0.90, CefSharp/SchemeHandler/FolderSchemeHandlerFactory.cs used filePath.StartsWith(rootFolder, StringComparison.OrdinalIgnoreCase) to decide whether a decoded and canonicalized request path remained inside rootFolder. That raw prefix test did not enforce a directory boundary, so a request such as ..%2fwww2/secret.txt could escape a configured www directory into a sibling www2 directory whose path shared the same string prefix. Applications that register FolderSchemeHandlerFactory for a custom scheme or an HTTP or HTTPS scheme can therefore serve local files outside the intended root when an attacker can cause the embedded browser to request the crafted URL. The issue affects both Unix-style paths such as /tmp/app/www2 and Windows paths such as C:\app\www2, and the fix appends a directory separator to the normalized root before comparison while rejecting null bytes and alternate data stream syntax. This issue is fixed in version 148.0.90.

Source published

18 Aug 2026 22:16:52 UTC

Source modified

9 Nov 2026 20:10:00 UTC

Saved here

10 Nov 2026 16:25:45 UTC

Source terms

NIST NVD usage terms; underlying source attribution retained

Original source record · Cite this exact observation · Complete original publisher JSON

Source: nvd · NIST NVD usage terms; underlying source attribution retained. The publisher's wording is preserved. ChangeIntel groups the information and labels changes. The JSON record includes additional source fields.

CVSS 3.1 · [email protected] · Secondary · 5.3 CVSS:3.1/AV:N/AC:H/PR:N/UI:R/S:U/C:H/I:N/A:N

### Summary `FolderSchemeHandlerFactory` was intended to restrict served files to a configured `rootFolder`, but its path validation used a raw string prefix check. A request could escape to a sibling directory whose full path starts with the root folder path, allowing files outside the configured root to be served. ### Details In affected versions, `FolderSchemeHandlerFactory` canonicalized `rootFolder`, decoded the request path, combined it with the root, and then allowed the file when: ```csharp filePath.StartsWith(rootFolder, StringComparison.OrdinalIgnoreCase) ``` This does not enforce a directory boundary. For example, `/tmp/app/www2/secret.txt` starts with `/tmp/app/www`, but `www2` is a sibling of `www`, not a child. The same issue applies on Windows, for example `C:\app\www2\secret.txt` starts with `C:\app\www`. The affected code was reviewed at commit `b5fef3bb4bc58798c95170078c41de92cfe9066e`, assembly version `147.0.100`. ### PoC Set `rootFolder` to a directory named `www` and create a sibling directory named `www2`: ```text <temp>/www/index.html <temp>/www2/secret.txt ``` Register `FolderSchemeHandlerFactory` for `<temp>/www`, then request: ```text https://folderschemehandlerfactory.test/..%2fwww2/secret.txt ``` The request path is URL-decoded to `../www2/secret.txt`, combined with `<temp>/www`, and canonicalized to: ```text <temp>/www2/secret.txt ``` Because `<temp>/www2/secret.txt` starts with `<temp>/www` as a string prefix, the affected check passes and `secret.txt` is served from outside `rootFolder`. Expected vulnerable result: HTTP 200 with the contents of `<temp>/www2/secret.txt`. Expected fixed result: 404 or equivalent not-found response because the resolved file is outside `rootFolder`. ### Impact Applications using `FolderSchemeHandlerFactory` for a custom scheme or registered HTTP/HTTPS scheme may expose local files outside the intended served directory. This is most relevant when sensitive sibling directories share the root path prefix, such as `www`/`www2`, `public`/`public_backup`, or `static`/`static-secrets`. An attacker must be able to cause the embedded browser to request URLs handled by the affected scheme registration.

Source published

30 Jun 2026 18:36:12 UTC

Source modified

10 Sep 2026 03:51:08 UTC

Saved here

23 Oct 2026 16:01:25 UTC

Source terms

GitHub Advisory Database · CC-BY-4.0

Original source record · Cite this exact observation · Complete original publisher JSON

Source: osv · GitHub Advisory Database · CC-BY-4.0. The publisher's wording is preserved. ChangeIntel groups the information and labels changes. The JSON record includes additional source fields.

CVSS_V3 · CVSS:3.1/AV:N/AC:H/PR:N/UI:R/S:U/C:H/I:N/A:N

Publisher rating · MODERATE