CVE-2026-63890 in Linux
Summary
by MITRE • 07/19/2026
In the Linux kernel, the following vulnerability has been resolved:
scsi: fcoe: Reject FIP descriptors with zero fip_dlen in CVL walker
drivers/scsi/fcoe/fcoe_ctlr.c::fcoe_ctlr_recv_clr_vlink() advanced the descriptor cursor by an attacker-supplied fip_dlen without ever requiring dlen >= sizeof(struct fip_desc) in the default branch. The named descriptor cases (FIP_DT_MAC, FIP_DT_NAME, FIP_DT_VN_ID) checked their per-type minimum lengths, but a FIP_DT_NON_CRITICAL descriptor (fip_dtype >= 128, which the standard requires receivers to silently ignore) skipped that check entirely.
An unauthenticated L2 peer on the FCoE control VLAN could hang fcoe_ctlr_recv_work on an fcoe, qedf, or bnx2fc initiator indefinitely by emitting one FIP CVL frame whose single descriptor had fip_dtype == FIP_DT_NON_CRITICAL and fip_dlen == 0: the cursor advanced zero bytes per iteration and the loop condition rlen >= sizeof(*desc) stayed true forever, blocking every subsequent FIP frame on that controller.
Tighten the outer dlen guard to also reject dlen < sizeof(struct fip_desc), so a malformed descriptor whose length cannot even cover the descriptor header is rejected before the switch. This is the same lower-bound the named cases already apply and is the minimum scope that closes the loop.
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Analysis
by VulDB Data Team • 07/19/2026
The vulnerability resides in the Linux kernel's Fibre Channel over Ethernet (FCoE) implementation, specifically within the FCoE controller subsystem. This issue affects drivers scsi/fcoe/fcoe_ctlr.c through the fcoe_ctlr_recv_clr_vlink() function which processes FIP control frames received on the FCoE control VLAN. The flaw manifests when processing FIP descriptors with zero length fields, creating a potential denial of service condition that can indefinitely block FCoE operations.
The technical implementation flaw stems from inadequate validation of descriptor lengths within the FIP descriptor walker loop. While specific descriptor types such as FIP_DT_MAC, FIP_DT_NAME, and FIP_DT_VN_ID properly validate their minimum required lengths before processing, the FIP_DT_NON_CRITICAL descriptor type bypasses this crucial check entirely. This descriptor type is defined by the standard to have fip_dtype values >= 128 and should be silently ignored by receivers according to FCoE specifications. However, the implementation fails to enforce basic structural validation when these descriptors are encountered.
The operational impact of this vulnerability is significant for FCoE initiators using drivers such as fcoe, qedf, or bnx2fc. An unauthenticated peer on the Layer 2 network segment can exploit this weakness by crafting a single FIP CVL frame containing a malformed descriptor where fip_dtype equals FIP_DT_NON_CRITICAL and fip_dlen equals zero. This specific combination causes the descriptor cursor to advance by zero bytes in each iteration of the processing loop, while maintaining the loop condition rlen >= sizeof(*desc) as true indefinitely. The consequence is that the fcoe_ctlr_recv_work function becomes trapped in an endless loop, effectively blocking all subsequent FIP frames on that particular controller and rendering the FCoE initiator non-functional.
This vulnerability aligns with CWE-129 Input Validation and CWE-691 Insufficient Control Flow Management patterns, representing a classic buffer overread scenario where inadequate bounds checking leads to control flow manipulation. The flaw also maps to ATT&CK technique T1499.004 for Endpoint Denial of Service through resource exhaustion, as the attacker can consume system resources indefinitely without requiring authentication. The root cause demonstrates poor defensive programming practices where minimal validation is performed on input data structures before processing.
The proposed mitigation implements a stricter outer bounds check that validates descriptor length against the minimum required structure size before any processing occurs. This approach ensures that malformed descriptors whose length cannot accommodate even the basic descriptor header are rejected at the earliest possible point in the processing pipeline. The fix aligns the validation logic for all descriptor types, including FIP_DT_NON_CRITICAL, to require dlen >= sizeof(struct fip_desc) as already implemented for other descriptor types. This minimal scope correction effectively closes the loop while maintaining compatibility with existing valid FIP frame processing and adhering to established security principles of early input validation and defense in depth.