Summary
F´ versions before 4.3.0 allow Svc::FileUplink to use packet-controlled destination paths without canonicalization or confinement to an upload directory. A peer able to send file-uplink packets may create or overwrite files at attacker-selected writable locations, potentially affecting system integrity and availability.
F´ versions before 4.3.0 allow Svc::FileUplink to use packet-controlled destination paths without canonicalization or confinement to an upload directory. A peer able to send file-uplink packets may create or overwrite files at attacker-selected writable locations, potentially affecting system integrity and availability.
Affected context
The issue occurs in deployments using F´ Svc::FileUplink to process
Fw::FilePacket::StartPacket messages. Risk is present when a peer can send
file-uplink packets and the receiving process has write access beyond an
intended upload directory. Absolute paths, traversal sequences, or other
attacker-selected writable destinations may be accepted without adequate
canonicalization and confinement.
The issue occurs in deployments using F´ Svc::FileUplink to process
Fw::FilePacket::StartPacket messages. Risk is present when a peer can send
file-uplink packets and the receiving process has write access beyond an
intended upload directory. Absolute paths, traversal sequences, or other
attacker-selected writable destinations may be accepted without adequate
canonicalization and confinement.
Exploit preconditions
- Attack surface: F´ file-uplink packet handling
- Required access: Ability to send or cause processing of file-uplink packets
- Trigger point: Handling of a
StartPacketcontaining a destination path - Required runtime condition: The FileUplink process must have write access
to the selected filesystem location
- Why exploitation is possible: The destination path is taken from packet
data and opened for writing without reliable canonicalization or directory
confinement
- Attack surface: F´ file-uplink packet handling
- Required access: Ability to send or cause processing of file-uplink packets
- Trigger point: Handling of a
StartPacketcontaining a destination path - Required runtime condition: The FileUplink process must have write access
to the selected filesystem location
- Why exploitation is possible: The destination path is taken from packet
data and opened for writing without reliable canonicalization or directory
confinement
Why this happens
The underlying bug is an improper limitation of a pathname to a restricted
directory, mapping primarily to CWE-22: Improper Limitation of a Pathname to a Restricted Directory ('Path Traversal'). FileUplink trusts a
packet-controlled destination path and opens it before establishing that the
resolved path remains within an approved upload location. This permits absolute,
traversing, or otherwise attacker-selected paths to influence filesystem writes.
The underlying bug is an improper limitation of a pathname to a restricted
directory, mapping primarily to CWE-22: Improper Limitation of a Pathname to a Restricted Directory ('Path Traversal'). FileUplink trusts a
packet-controlled destination path and opens it before establishing that the
resolved path remains within an approved upload location. This permits absolute,
traversing, or otherwise attacker-selected paths to influence filesystem writes.
Potential impact
- An attacker may create files in writable filesystem locations
- Existing writable files may be overwritten or corrupted
- Application or mission data integrity could be affected
- Configuration or operational files may be disrupted if writable
- Service availability could be reduced through destructive or oversized writes
- An attacker may create files in writable filesystem locations
- Existing writable files may be overwritten or corrupted
- Application or mission data integrity could be affected
- Configuration or operational files may be disrupted if writable
- Service availability could be reduced through destructive or oversized writes
General mitigation guidance
Mitigation generally focuses on removing trust from packet-controlled paths
and enforcing a narrow filesystem boundary.
Common defensive patterns include:
- Resolving submitted paths against a fixed upload directory and rejecting
results that escape that directory
- Rejecting absolute paths, traversal components, ambiguous separators, and
links that bypass confinement
- Generating server-side filenames rather than accepting arbitrary destination
names
- Using allowlisted file destinations and safe file-creation semantics
- Running the FileUplink process with only the minimum required filesystem
permissions
- Applying read-only or isolated filesystem layouts where practical
- Treating uploaded content and metadata as untrusted until validation is
complete
Mitigation generally focuses on removing trust from packet-controlled paths
and enforcing a narrow filesystem boundary.
Common defensive patterns include:
- Resolving submitted paths against a fixed upload directory and rejecting
results that escape that directory
- Rejecting absolute paths, traversal components, ambiguous separators, and
links that bypass confinement
- Generating server-side filenames rather than accepting arbitrary destination
names
- Using allowlisted file destinations and safe file-creation semantics
- Running the FileUplink process with only the minimum required filesystem
permissions
- Applying read-only or isolated filesystem layouts where practical
- Treating uploaded content and metadata as untrusted until validation is
complete
How teams detect issues like this
Detection can combine static analysis, review, testing, and runtime controls:
- Search for packet, request, or message fields passed directly to filesystem
open, create, rename, or overwrite operations
- Flag path concatenation that lacks canonicalization and containment checks
- Review handling of absolute paths,
..segments, symbolic links, and platform
specific path forms
- Add tests confirming that resolved paths cannot escape the designated upload
directory
- Enforce policies requiring allowlisted directories and least-privilege service
accounts
- Monitor file creation and modification outside expected upload locations
Automated security analysis and code-review tools may help identify these patterns
during development.
Detection can combine static analysis, review, testing, and runtime controls:
- Search for packet, request, or message fields passed directly to filesystem
open, create, rename, or overwrite operations
- Flag path concatenation that lacks canonicalization and containment checks
- Review handling of absolute paths,
..segments, symbolic links, and platform
specific path forms
- Add tests confirming that resolved paths cannot escape the designated upload
directory
- Enforce policies requiring allowlisted directories and least-privilege service
accounts
- Monitor file creation and modification outside expected upload locations
Automated security analysis and code-review tools may help identify these patterns
during development.
