Description

In the Linux kernel, the following vulnerability has been resolved: scsi: libiscsi_tcp: Bound SCSI Response data segment to the connection buffer iscsi_tcp_hdr_dissect() receives the data segment of several PDU types into the fixed-size conn->data buffer, which is allocated for ISCSI_DEF_MAX_RECV_SEG_LEN (8192) bytes. For the LOGIN_RSP, TEXT_RSP, REJECT and ASYNC_EVENT opcodes the dissect path already rejects a PDU whose DataSegmentLength exceeds that buffer. The SCSI Command Response (ISCSI_OP_SCSI_CMD_RSP) path also copies its data segment (sense/response data) into conn->data via iscsi_tcp_data_recv_prep(), but it does so without the same check. The only upstream bound on in.datalen is conn->max_recv_dlength, the initiator's advertised MaxRecvDataSegmentLength, which is commonly negotiated well above 8192 (open-iscsi defaults to 262144). A target that returns a SCSI Response with a DataSegmentLength between 8193 and max_recv_dlength therefore overflows the 8192-byte conn->data buffer. Once the same bound applies, ISCSI_OP_SCSI_CMD_RSP is handled exactly like those responses: bound the data segment, receive it into conn->data when present, and otherwise complete the PDU with no data. Fold the opcode into that case group rather than duplicating the check.

Executive Summary

Technical Details

Mitigations

References

Additional Metadata

{
  "score": "9.8",
  "pubDate": "2026-08-15T13:18:01.047Z",
  "pubdate": "2026-08-15T13:18:01.047Z",
  "executiveSummary": "A buffer overflow vulnerability exists in the Linux kernel iSCSI TCP subsystem, specifically within the libiscsi_tcp module. The flaw resides in the handling of SCSI Command Response (ISCSI_OP_SCSI_CMD_RSP) Protocol Data Units (PDUs) within the iscsi_tcp_hdr_dissect() function. Due to a missing validation check on the incoming DataSegmentLength against the fixed-size connection data buffer, a malicious or compromised iSCSI target can transmit a crafted SCSI Response containing an oversized data segment. This condition leads to an out-of-bounds memory copy, overwriting the conn->data buffer allocated for ISCSI_DEF_MAX_RECV_SEG_LEN (8192) bytes. Successful exploitation of this vulnerability can result in kernel memory corruption, leading to system crashes, denial of service, or potentially arbitrary code execution within kernel space. The attack requires a network-accessible iSCSI target capable of communicating with the initiator and sending malicious responses during the iSCSI session. The risk is elevated in environments where initiators connect to untrusted storage targets operating over networks without adequate authentication or encryption controls.",
  "technicalDetails": "The vulnerability is rooted in insufficient bounds checking within the Linux kernel's iSCSI TCP transport implementation, specifically in the file drivers/scsi/libiscsi_tcp.c. The function iscsi_tcp_hdr_dissect() is responsible for receiving and processing the data segments of various PDU types into a fixed-size connection buffer, designated as conn->data, which is statically allocated to accommodate ISCSI_DEF_MAX_RECV_SEG_LEN (8192) bytes. While other PDU opcodes such as LOGIN_RSP, TEXT_RSP, REJECT, and ASYNC_EVENT include explicit validation logic to reject PDUs whose DataSegmentLength exceeds the fixed buffer size, the handler for ISCSI_OP_SCSI_CMD_RSP lacks this critical validation check. During the parsing of SCSI Command Responses, the subsystem invokes iscsi_tcp_data_recv_prep() to copy sense or response data directly into conn->data without verifying the length against the actual buffer allocation. Instead, the only upstream boundary enforced is in.datalen, which is governed by conn->max_recv_dlength—the initiator's advertised MaxRecvDataSegmentLength parameter. This parameter is commonly negotiated to significantly larger values, such as the open-iscsi default of 262144 bytes. An attacker operating a malicious iSCSI target can craft a SCSI Response PDU with a DataSegmentLength ranging between 8193 and max_recv_dlength bytes. When the vulnerable initiator parses this response, the incoming data stream overflows the 8192-byte conn->data buffer. Step-by-step, the attack flow proceeds as follows: first, an iSCSI session is established between the initiator and the target; second, the target sends a malicious ISCSI_OP_SCSI_CMD_RSP PDU with an inflated DataSegmentLength field; third, the initiator's iscsi_tcp_hdr_dissect() processes the PDU header without validating the segment length against the local buffer size limit; fourth, the subsystem attempts to copy the excessive payload into conn->data, resulting in a heap-based buffer overflow in kernel memory. This corruption can destabilize the kernel, precipitate a kernel panic, or corrupt adjacent kernel data structures, depending on memory layout and slab allocation specifics."
}