CVE-2026-55668

File Browser provides a web file managing interface. Prior to 2.63.16, ScopedFs validates the nearest existing ancestor of a dangling symlink as in scope and then follows the symlink during file creation, allowing an authenticated user with Create and Modify permissions to create attacker-controlled files outside the user's scope. This issue is fixed in version 2.63.16.

File Browser provides a web file managing interface. Prior to 2.63.16, ScopedFs validates the nearest existing ancestor of a dangling symlink as in scope and then follows the symlink during file creation, allowing an authenticated user with Create and Modify permissions to create attacker-controlled files outside the user's scope. This issue is fixed in version 2.63.16.

Summary

ScopedFs confines every File Browser user to a scope directory. Its within() guard is meant to reject any operation that follows a symbolic link out of that scope. When the link target does not exist yet, the guard walks up to the nearest existing ancestor and validates that instead. For a dangling symlink (target does not exist), the nearest existing ancestor is the in-scope directory containing the link, so the guard returns "in scope" and the subsequent os.OpenFile(O_CREATE) follows the link and creates the file at its out-of-scope target.

A post-auth user with Create and Modify permission can write attacker-controlled content to any non-existent path outside their scope that the File Browser process can write to. The precondition is a dangling symlink present inside the user's scope, which is the same out-of-band precondition the rest of ScopedFs is built to defend against.

This is a patch-gap variant of the GHSA-239w-m3h6-ch8v symlink confinement issue, not a resubmission of the already-published vulnerable-version behavior: GHSA-239w-m3h6-ch8v marks <= 2.63.13 vulnerable and 2.63.14 patched, while this proof reproduces on current master / v2.63.15 (be23ab3a15bf957928ecfed88de5ab67850c1b9c). The escaping-symlink-to-an-existing-target case is defended and tested. The dangling case is neither, and the gap is acknowledged in a code comment as "best-effort".

Root cause

files/scoped.go (commit be23ab3). The guard, including the maintainer comment that already flags this exact gap:

// Note: a dangling symlink whose target does not yet exist resolves to its
// containing directory and is therefore allowed; writing through such a link
// could still create a file outside the scope. This is treated as best-effort
// and relies on rejecting existing escaping symlinks, which covers the
// disclosure and overwrite vectors.
func (s *ScopedFs) within(p string) (bool, error) {
    root, err := filepath.EvalSymlinks(afero.FullBaseFsPath(s.base, "/"))
    if err != nil {
        return false, err
    }

    target := afero.FullBaseFsPath(s.base, p)
    resolved, err := filepath.EvalSymlinks(target)
    for errors.Is(err, fs.ErrNotExist) {
        parent := filepath.Dir(target)   // LEXICAL parent of the link path
        if parent == target {
            break
        }
        target = parent
        resolved, err = filepath.EvalSymlinks(target)
    }
    if err != nil {
        return false, err
    }
    // ...
    return resolved == root || strings.HasPrefix(resolved, prefix), nil
}

When p is a symlink whose target does not exist, EvalSymlinks(target) returns fs.ErrNotExist. The loop takes the lexical parent of the link path (filepath.Dir), a real directory inside the scope, and EvalSymlinks of that resolves under the scope root. within() returns true and guard() permits the operation. The write then dereferences the link at the OS layer:

func (s *ScopedFs) OpenFile(name string, flag int, perm os.FileMode) (afero.File, error) {
    if err := s.guard(name); err != nil {   // returns nil for a dangling escaping symlink
        return nil, err
    }
    return s.base.OpenFile(name, flag, perm) // os.OpenFile(O_CREATE) follows the link
}

The assumption that breaks: within() treats "target does not exist" as "brand-new in-scope file" and validates the containing directory. But the path component being created is itself a symlink pointing outside the scope. O_CREATE follows it and creates the file at the link target, not inside the validated directory. The existing-target case is correctly blocked, because the walk-up resolves the link itself to an out-of-scope path. Only the dangling case slips through.

For the layout below:

/tmp/root/scope/escape -> /tmp/root/outside/created-by-http.txt
/tmp/root/outside/                      # exists
/tmp/root/outside/created-by-http.txt   # does not exist yet

EvalSymlinks(/tmp/root/scope/escape)…

File Browser provides a web file managing interface. Prior to 2.63.16, ScopedFs validates the nearest existing ancestor of a dangling symlink as in scope and then follows the symlink during file creation, allowing an authenticated user with Create and Modify permissions to create attacker-controlled files outside the user's scope. This issue is fixed in version 2.63.16.

File Browser provides a web file managing interface. Prior to 2.63.16, ScopedFs validates the nearest existing ancestor of a dangling symlink as in scope and then follows the symlink during file creation, allowing an authenticated user with Create and Modify permissions to create attacker-controlled files outside the user's scope. This issue is fixed in version 2.63.16.

Summary

ScopedFs confines every File Browser user to a scope directory. Its within() guard is meant to reject any operation that follows a symbolic link out of that scope. When the link target does not exist yet, the guard walks up to the nearest existing ancestor and validates that instead. For a dangling symlink (target does not exist), the nearest existing ancestor is the in-scope directory containing the link, so the guard returns "in scope" and the subsequent os.OpenFile(O_CREATE) follows the link and creates the file at its out-of-scope target.

A post-auth user with Create and Modify permission can write attacker-controlled content to any non-existent path outside their scope that the File Browser process can write to. The precondition is a dangling symlink present inside the user's scope, which is the same out-of-band precondition the rest of ScopedFs is built to defend against.

This is a patch-gap variant of the GHSA-239w-m3h6-ch8v symlink confinement issue, not a resubmission of the already-published vulnerable-version behavior: GHSA-239w-m3h6-ch8v marks <= 2.63.13 vulnerable and 2.63.14 patched, while this proof reproduces on current master / v2.63.15 (be23ab3a15bf957928ecfed88de5ab67850c1b9c). The escaping-symlink-to-an-existing-target case is defended and tested. The dangling case is neither, and the gap is acknowledged in a code comment as "best-effort".

Root cause

files/scoped.go (commit be23ab3). The guard, including the maintainer comment that already flags this exact gap:

// Note: a dangling symlink whose target does not yet exist resolves to its
// containing directory and is therefore allowed; writing through such a link
// could still create a file outside the scope. This is treated as best-effort
// and relies on rejecting existing escaping symlinks, which covers the
// disclosure and overwrite vectors.
func (s *ScopedFs) within(p string) (bool, error) {
    root, err := filepath.EvalSymlinks(afero.FullBaseFsPath(s.base, "/"))
    if err != nil {
        return false, err
    }

    target := afero.FullBaseFsPath(s.base, p)
    resolved, err := filepath.EvalSymlinks(target)
    for errors.Is(err, fs.ErrNotExist) {
        parent := filepath.Dir(target)   // LEXICAL parent of the link path
        if parent == target {
            break
        }
        target = parent
        resolved, err = filepath.EvalSymlinks(target)
    }
    if err != nil {
        return false, err
    }
    // ...
    return resolved == root || strings.HasPrefix(resolved, prefix), nil
}

When p is a symlink whose target does not exist, EvalSymlinks(target) returns fs.ErrNotExist. The loop takes the lexical parent of the link path (filepath.Dir), a real directory inside the scope, and EvalSymlinks of that resolves under the scope root. within() returns true and guard() permits the operation. The write then dereferences the link at the OS layer:

func (s *ScopedFs) OpenFile(name string, flag int, perm os.FileMode) (afero.File, error) {
    if err := s.guard(name); err != nil {   // returns nil for a dangling escaping symlink
        return nil, err
    }
    return s.base.OpenFile(name, flag, perm) // os.OpenFile(O_CREATE) follows the link
}

The assumption that breaks: within() treats "target does not exist" as "brand-new in-scope file" and validates the containing directory. But the path component being created is itself a symlink pointing outside the scope. O_CREATE follows it and creates the file at the link target, not inside the validated directory. The existing-target case is correctly blocked, because the walk-up resolves the link itself to an out-of-scope path. Only the dangling case slips through.

For the layout below:

/tmp/root/scope/escape -> /tmp/root/outside/created-by-http.txt
/tmp/root/outside/                      # exists
/tmp/root/outside/created-by-http.txt   # does not exist yet

EvalSymlinks(/tmp/root/scope/escape)…

File Browser: ScopedFs follows a dangling symlink on write, letting a scoped user create files outside their scope in github.com/filebrowser/filebrowser

This update for govulncheck-vulndb fixes the following issues:

• Update to version 0.0.20260723T184607 2026-07-23T18:46:07Z (jsc#PED-11136).

Go CVE Numbering Authority IDs added or updated with aliases:

• GO-2026-4730 CVE-2026-33022 GHSA-cv4x-93xx-wgfj
• GO-2026-4761 CVE-2026-33211 GHSA-j5q5-j9gm-2w5c
• GO-2026-5102 CVE-2026-45021 GHSA-3vcp-chfh-f6r2
• GO-2026-5272 CVE-2026-40938 GHSA-94jr-7pqp-xhcq
• GO-2026-5486 CVE-2026-40924 GHSA-m2cx-gpqf-qf74
• GO-2026-5542 CVE-2026-40090 GHSA-pj97-4p9w-gx3q
• GO-2026-5630 CVE-2026-25542 GHSA-rmx9-2pp3-xhcr
• GO-2026-5643 CVE-2026-40923 GHSA-rx35-6rhx-7858
• GO-2026-5675 CVE-2026-41492 GHSA-vvf7-6rmr-m29q
• GO-2026-5711 CVE-2026-40161 GHSA-wjxp-xrpv-xpff
• GO-2026-5746 CVE-2026-41567 GHSA-x86f-5xw2-fm2r
• GO-2026-5749 CVE-2026-41328 GHSA-x92x-px7w-4gx4
• GO-2026-5837 CVE-2026-44840 GHSA-q2m9-6jp9-c6mc
• GO-2026-5929 CVE-2026-44342 GHSA-26v7-h57m-gh9m
• GO-2026-5930 CVE-2026-33655 GHSA-6qcr-qxgr-m7fv
• GO-2026-5933 GHSA-3g4q-2f67-2gvh
• GO-2026-5934 GHSA-59qp-cfj3-rp64
• GO-2026-5935 GHSA-7856-g3gv-9wq8
• GO-2026-5936 CVE-2026-53552 GHSA-26rh-24rg-j3vv
• GO-2026-5937 CVE-2026-53508 GHSA-2jcc-mxv7-p3f9
• GO-2026-5938 CVE-2026-53553 GHSA-4g5x-hcwm-82jw
• GO-2026-5939 CVE-2026-10517 GHSA-698x-9w2p-7vvp
• GO-2026-5940 CVE-2026-53572 GHSA-6w3m-4hhp-775q
• GO-2026-5941 CVE-2026-53487 GHSA-gvhc-wv3v-7pf8
• GO-2026-5942 CVE-2026-46600
• GO-2026-5944 CVE-2026-50197 GHSA-659f-rgp5-w4wf
• GO-2026-5945 CVE-2026-6815 GHSA-rmxx-v9rj-vpvg
• GO-2026-5946 CVE-2026-52831 GHSA-v5px-423j-pf7p
• GO-2026-5947 CVE-2026-53649 GHSA-xqhv-chqm-fhcc
• GO-2026-5948 CVE-2026-50554 GHSA-588f-fvcv-xhvf
• GO-2026-5949 CVE-2026-50553 GHSA-rqrh-8wpv-x7hh
• GO-2026-5950 CVE-2026-53602 GHSA-339v-266x-79xr
• GO-2026-5951 CVE-2026-10219 GHSA-6jm8-4fhr-5w64
• GO-2026-5952 CVE-2026-49834 GHSA-9vcr-p3rj-q5q6
• GO-2026-5953 CVE-2026-9094 GHSA-c9w5-qp6m-m395
• GO-2026-5956 CVE-2026-55252 GHSA-h5g6-xmh4-hc37
• GO-2026-5957 CVE-2026-54158 GHSA-5xfx-xj4h-5p7r
• GO-2026-5958 CVE-2026-54068 GHSA-gcm7-57gf-953c
• GO-2026-5959 CVE-2026-54072 GHSA-h29v-hj44-q8cv
• GO-2026-5961 CVE-2026-54069 GHSA-hvr9-72v2-fff3
• GO-2026-5962 CVE-2026-54088 GHSA-m93h-4hw7-5qcm
• GO-2026-5963 CVE-2026-54067 GHSA-mvjr-vv3c-w4qv
• GO-2026-5964 CVE-2026-54066 GHSA-p4m3-mgmm-c664
• GO-2026-5965 CVE-2026-54070 GHSA-w7cg-whh7-xp28
• GO-2026-5966 CVE-2026-54089 GHSA-xqp3-jq6g-x3qm
• GO-2026-5967 CVE-2026-50551 GHSA-56mp-4f3v-fgj2
• GO-2026-5968 CVE-2026-54174 GHSA-fpg8-7664-jc5q
• GO-2026-5969 GHSA-g936-7jqj-mwv8
• GO-2026-5970 CVE-2026-56852
• GO-2026-5973 CVE-2026-54250 GHSA-jxr7-mqhw-9p98
• GO-2026-5974 CVE-2026-44300 GHSA-wmj8-9953-vff5
• GO-2026-5975 CVE-2026-50018 GHSA-42j2-w334-qxw7
• GO-2026-5976 CVE-2026-50141 GHSA-g7mm-9vx7-jm7h
• GO-2026-5977 CVE-2026-50013 GHSA-qrh4-p6v4-mrfg
• GO-2026-5978 CVE-2026-50125 GHSA-qw5r-ppcg-f8rj
• GO-2026-5979 CVE-2026-50006 GHSA-xrcf-6jh3-ggvx
• GO-2026-5980 CVE-2026-50158 GHSA-2c7f-fxww-6w6c
• GO-2026-5981 GHSA-mqxv-9rm6-w8qc
• GO-2026-5982 GHSA-pqg7-v6wh-3pfp
• GO-2026-5984 CVE-2026-53604 GHSA-2p2f-px33-4vv5
• GO-2026-5985 GHSA-7rx3-5wx3-5v76
• GO-2026-5986 CVE-2026-61699 GHSA-cm26-5974-52h8
• GO-2026-5987 CVE-2026-55513 GHSA-g4x6-jcvr-9m3g
• GO-2026-5988 CVE-2026-54628 GHSA-hwrq-8wxh-q4xv
• GO-2026-5989 CVE-2026-55512 GHSA-m3cx-mwpg-32jg
• GO-2026-5990 CVE-2026-54629 GHSA-mf78-3rpf-r784
• GO-2026-5991 CVE-2026-53603 GHSA-q4vm-pq3q-8wgq
• GO-2026-5992 CVE-2026-61549 GHSA-qf34-295c-26v8
• GO-2026-5996 CVE-2026-54450 GHSA-pph6-vfjv-vpjw
• GO-2026-5997 CVE-2026-54452 GHSA-xgch-x3mx-cm3c
• GO-2026-5998 CVE-2026-54495 GHSA-398h-7f66-3h4p
• GO-2026-5999 CVE-2026-10814 GHSA-jh6h-v6mp-h22v
• GO-2026-6002 CVE-2026-58196 GHSA-pr64-jmmf-jp54
• GO-2026-6003 CVE-2026-53714 GHSA-22xc-xg2r-9j7v
• GO-2026-6004 CVE-2026-52833 GHSA-3v79-m2cg-89ww
• GO-2026-6005 CVE-2026-53715 GHSA-8fv2-88gg-hm7q
• GO-2026-6006 CVE-2026-53716 GHSA-cxpq-8v7q-cg56 *…