CVE-2026-55825

Contao is an Open Source CMS. In versions 5.7.0 through 5.7.6, an authenticated backend user who can access one job can request an attachment identifier containing ../ segments and make the job attachment download endpoint read a file from another job directory inside var/job-attachments. The controller authorizes only the jobUuid route parameter. The later attachment lookup joins that authorized job UUID with the attacker-controlled identifier, then passes the combined path to the virtual filesystem. VirtualFilesystem::resolve() canonicalizes the whole path and only rejects paths that escape the filesystem mount, so authorized-job/../victim-job/debug_log.csv becomes victim-job/debug_log.csv. This is a cross-job authorization bypass for known job attachment paths. It is not a practical brute-force against unknown jobs because job directories are UUID v4 values.

Contao is an Open Source CMS. In versions 5.7.0 through 5.7.6, an authenticated backend user who can access one job can request an attachment identifier containing ../ segments and make the job attachment download endpoint read a file from another job directory inside var/job-attachments. The controller authorizes only the jobUuid route parameter. The later attachment lookup joins that authorized job UUID with the attacker-controlled identifier, then passes the combined path to the virtual filesystem. VirtualFilesystem::resolve() canonicalizes the whole path and only rejects paths that escape the filesystem mount, so authorized-job/../victim-job/debug_log.csv becomes victim-job/debug_log.csv. This is a cross-job authorization bypass for known job attachment paths. It is not a practical brute-force against unknown jobs because job directories are UUID v4 values.

Summary

An authenticated backend user who can access one job can request an attachment identifier containing ../ segments and make the job attachment download endpoint read a file from another job directory inside var/job-attachments.

The controller authorizes only the jobUuid route parameter. The later attachment lookup joins that authorized job UUID with the attacker-controlled identifier, then passes the combined path to the virtual filesystem. VirtualFilesystem::resolve() canonicalizes the whole path and only rejects paths that escape the filesystem mount, so authorized-job/../victim-job/debug_log.csv becomes victim-job/debug_log.csv.

This is a cross-job authorization bypass for known job attachment paths. It is not a practical brute-force against unknown jobs because job directories are UUID v4 values.

Root Cause

JobsController::downloadJobAttachment() checks access to the route jobUuid before loading the attachment:

$job = $this->jobs->getByUuid($jobUuid);

if (!$job || !$this->jobs->hasAccess($job)) {
    throw $this->createNotFoundException();
}

$attachment = $this->jobs->getAttachment($jobUuid, $identifier);

Jobs::getAttachment() then resolves a path built from the authorized job UUID and the attacker-controlled identifier:

$fileItem = $this->jobAttachmentsStorage->get($this->getAttachmentIdentifier($job, $identifier));

return $job->getUuid().'/'.$identifier;

VirtualFilesystem::resolve() canonicalizes the combined path. It rejects absolute paths and paths that start with .., but it does not preserve the authorized job directory as a boundary:

$path = Path::canonicalize($location);

if (str_starts_with($path, '..')) {
    throw new \OutOfBoundsException(...);
}

return Path::join($this->prefix, $path);

Therefore:

<authorized-job>/../<victim-job>/debug_log.csv

canonicalizes to:

<victim-job>/debug_log.csv

which remains inside the job-attachments filesystem mount and is accepted.

Recommended Fix

Treat the attachment identifier as a filename, not a path:

• Reject /, \, NUL, and dot-segment components in identifier.
• Add a route requirement that prevents slashes in {identifier} if nested attachment paths are not intended.
• After resolving, assert the canonical relative path starts with <authorized-job-uuid>/ before returning a FilesystemItem.
• Apply the same identifier validation in Jobs::addAttachment() so future producers/extensions cannot write outside the owning job directory.

Impact

A low-privileged backend user can read another job's attachment if they know or obtain the target job UUID and attachment filename. Built-in crawler jobs attach CSV logs such as debug_log.csv, broken-link-checker_log.csv, and search-index_log.csv, which can contain crawled URLs, referring URLs, tags, and error messages.

Contao is an Open Source CMS. In versions 5.7.0 through 5.7.6, an authenticated backend user who can access one job can request an attachment identifier containing ../ segments and make the job attachment download endpoint read a file from another job directory inside var/job-attachments. The controller authorizes only the jobUuid route parameter. The later attachment lookup joins that authorized job UUID with the attacker-controlled identifier, then passes the combined path to the virtual filesystem. VirtualFilesystem::resolve() canonicalizes the whole path and only rejects paths that escape the filesystem mount, so authorized-job/../victim-job/debug_log.csv becomes victim-job/debug_log.csv. This is a cross-job authorization bypass for known job attachment paths. It is not a practical brute-force against unknown jobs because job directories are UUID v4 values.

Contao is an Open Source CMS. In versions 5.7.0 through 5.7.6, an authenticated backend user who can access one job can request an attachment identifier containing ../ segments and make the job attachment download endpoint read a file from another job directory inside var/job-attachments. The controller authorizes only the jobUuid route parameter. The later attachment lookup joins that authorized job UUID with the attacker-controlled identifier, then passes the combined path to the virtual filesystem. VirtualFilesystem::resolve() canonicalizes the whole path and only rejects paths that escape the filesystem mount, so authorized-job/../victim-job/debug_log.csv becomes victim-job/debug_log.csv. This is a cross-job authorization bypass for known job attachment paths. It is not a practical brute-force against unknown jobs because job directories are UUID v4 values.

Summary

An authenticated backend user who can access one job can request an attachment identifier containing ../ segments and make the job attachment download endpoint read a file from another job directory inside var/job-attachments.

The controller authorizes only the jobUuid route parameter. The later attachment lookup joins that authorized job UUID with the attacker-controlled identifier, then passes the combined path to the virtual filesystem. VirtualFilesystem::resolve() canonicalizes the whole path and only rejects paths that escape the filesystem mount, so authorized-job/../victim-job/debug_log.csv becomes victim-job/debug_log.csv.

This is a cross-job authorization bypass for known job attachment paths. It is not a practical brute-force against unknown jobs because job directories are UUID v4 values.

Root Cause

JobsController::downloadJobAttachment() checks access to the route jobUuid before loading the attachment:

$job = $this->jobs->getByUuid($jobUuid);

if (!$job || !$this->jobs->hasAccess($job)) {
    throw $this->createNotFoundException();
}

$attachment = $this->jobs->getAttachment($jobUuid, $identifier);

Jobs::getAttachment() then resolves a path built from the authorized job UUID and the attacker-controlled identifier:

$fileItem = $this->jobAttachmentsStorage->get($this->getAttachmentIdentifier($job, $identifier));

return $job->getUuid().'/'.$identifier;

VirtualFilesystem::resolve() canonicalizes the combined path. It rejects absolute paths and paths that start with .., but it does not preserve the authorized job directory as a boundary:

$path = Path::canonicalize($location);

if (str_starts_with($path, '..')) {
    throw new \OutOfBoundsException(...);
}

return Path::join($this->prefix, $path);

Therefore:

<authorized-job>/../<victim-job>/debug_log.csv

canonicalizes to:

<victim-job>/debug_log.csv

which remains inside the job-attachments filesystem mount and is accepted.

Recommended Fix

Treat the attachment identifier as a filename, not a path:

• Reject /, \, NUL, and dot-segment components in identifier.
• Add a route requirement that prevents slashes in {identifier} if nested attachment paths are not intended.
• After resolving, assert the canonical relative path starts with <authorized-job-uuid>/ before returning a FilesystemItem.
• Apply the same identifier validation in Jobs::addAttachment() so future producers/extensions cannot write outside the owning job directory.

Impact

A low-privileged backend user can read another job's attachment if they know or obtain the target job UUID and attachment filename. Built-in crawler jobs attach CSV logs such as debug_log.csv, broken-link-checker_log.csv, and search-index_log.csv, which can contain crawled URLs, referring URLs, tags, and error messages.