CVE-2026-63889 in Linux
Summary
by MITRE • 07/19/2026
In the Linux kernel, the following vulnerability has been resolved:
scsi: scsi_transport_fc: Widen FPIN pname walker counter to u32
An adjacent Fibre Channel fabric actor that can deliver an FPIN ELS frame to an lpfc or qla2xxx Linux initiator can trigger a non-return in the generic FC transport. This is not a local userspace or IP network path; the attacker must be able to inject fabric traffic, for example as a compromised switch or fabric controller, or as a same-zone N_Port on a fabric that permits source spoofing.
The Link-Integrity and Peer-Congestion FPIN walkers used a u8 loop counter against the 32-bit on-wire pname_count field, and did not bound pname_count by the descriptor body already validated by the TLV walker. A pname_count of 256 therefore wraps the counter and keeps the loop condition true indefinitely.
Factor the shared pname_list[] walk into one helper, widen the counter
to u32, and clamp pname_count against the entries that fit in the descriptor body before iterating.
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Analysis
by VulDB Data Team • 07/19/2026
The vulnerability resides within the Linux kernel's Fibre Channel transport implementation, specifically affecting the scsi_transport_fc subsystem. This issue impacts lpfc and qla2xxx drivers that handle Fibre Channel communication between storage initiators and targets. The flaw manifests as a potential denial of service condition that can cause indefinite looping in the fabric protocol information (FPIN) processing mechanism, ultimately leading to system instability or complete system hang.
The technical root cause involves a counter overflow condition within the FPIN ELS frame processing logic where the loop counter variable was defined as an 8-bit unsigned integer (u8) while the on-wire pname_count field contains 32-bit information. This mismatch creates a scenario where a malicious fabric actor can craft an FPIN frame with a pname_count value of 256 or higher, causing the u8 counter to wrap around and maintain a true loop condition indefinitely. The vulnerability exists because the code path does not properly validate or bound the pname_count value against the actual descriptor body length that was already validated by the TLV (Type-Length-Value) walker component.
The operational impact of this vulnerability extends beyond simple denial of service as it creates a persistent system instability that can affect storage connectivity and overall system availability. Attackers must have access to fabric traffic injection capabilities, typically requiring compromise of fabric switches or controllers, or access to same-zone N_Ports within fabrics that permit source address spoofing. This attack vector aligns with ATT&CK technique T1566.002 for credential access through network boundary bridging and represents a sophisticated supply chain or infrastructure compromise scenario.
The fix implemented addresses this by refactoring the shared pname_list[] walking logic into a dedicated helper function, widening the loop counter from u8 to u32 type, and adding proper bounds checking that clamps the pname_count value against the actual descriptor body entries before iteration begins. This approach follows security best practices for preventing integer overflow conditions and aligns with CWE-190 which addresses integer overflow and wraparound issues. The mitigation strategy ensures that even if malicious data is injected into the fabric protocol, the system will not enter infinite loops but instead properly handle or reject malformed FPIN frames through bounded iteration and proper input validation.
This vulnerability demonstrates the importance of proper input validation in kernel space networking code where external fabric actors can influence system behavior through legitimate protocol mechanisms. The fix represents a defensive programming approach that prevents arithmetic overflow conditions while maintaining compatibility with existing valid FPIN frame formats, ensuring robust operation against both benign and malicious fabric traffic inputs.