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CVE-2026-74556
scsi: libiscsi_tcp: Bound SCSI Response data segment to the connection buffer
Published 2026-08-15 (2 months ago) by the Linux kernel CNA. Subsystem drivers/scsi. Debian urgency: not yet assigned.
What to do, per Debian release
Debian's own status for CVE-2026-74556 in every release this site tracks, and what each one means in practice. Every status below is the one the Debian Security Team publishes for this CVE. source
| Release | Status | Version | What this means |
|---|---|---|---|
| Debian 12bookworm | fixedDLA-4777-1 · 2026-09-08 · text | 6.1.187-1 | Update the kernel and reboot. DLA-4777-1 shipped the fix on 2026-09-08, in 6.1.187-1. A running kernel keeps the old code until the machine restarts. |
| Debian 13trixie | fixedDSA-6466-1 · 2026-08-25 · text | 6.12.105-1 | Update the kernel and reboot. DSA-6466-1 shipped the fix on 2026-08-25, in 6.12.105-1. A running kernel keeps the old code until the machine restarts. |
| Debian 14forky | fixed | 7.1.8-1 | Update the kernel and reboot. Fixed in 7.1.8-1. A running kernel keeps the old code until the machine restarts. |
| Debian unstablesid | fixed | 7.1.8-1 | Update the kernel and reboot. Fixed in 7.1.8-1. A running kernel keeps the old code until the machine restarts. |
| Debian 12bookworm · linux-6.12 | fixedDLA-4788-1 · 2026-09-19 · text | 6.12.107-1~deb12u1 | Update the kernel and reboot. DLA-4788-1 shipped the fix on 2026-09-19, in 6.12.107-1~deb12u1. A running kernel keeps the old code until the machine restarts. |
The vulnerability
What the bug is
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.
Where it lives
The fix touches these files. If the subsystem is one you do not use, the practical exposure is lower, though the package is still the vulnerable one.
drivers/scsi/libiscsi_tcp.c
- What this is
- ISCSIMAINTAINERS section matched on drivers/scsi/*iscsi* · open-iscsi@googlegroups.com · Maintained
- Kernel module
- libiscsi_tcp
Check it on the machine
grep -wE 'CONFIG_ISCSI_TCP|CONFIG_SCSI_CXGB3_ISCSI|CONFIG_SCSI_CXGB4_ISCSI' /boot/config-$(uname -r)Reads the booted kernel's own configuration, on the machine and nowhere else. =y is built in, =m is a module, and an is not set line means the code is not there.
lsmod | grep -w libiscsi_tcpPrints a line if that module is loaded right now, and nothing if it is not. One that is not loaded can still be loaded later by anything that needs it.
Show whether Debian builds this, per release
Debian builds this, but not on every flavour. At least one release below builds the code on some of its kernel flavours and not on others, so the answer depends on the architecture and flavour installed.
- bookwormMnot built on amd64/cloud-amd64, arm64/cloud-arm64
- trixieMnot built on amd64/cloud-amd64, arm64/cloud-arm64, armel/rpi
- forky, sid, bookworm · linux-6.12Mnot built on amd64/cloud-amd64, arm64/cloud-arm64
- M
- a module where it is built at all; some flavours do not build it
- Build switches
- CONFIG_ISCSI_TCP, CONFIG_SCSI_CXGB3_ISCSI, CONFIG_SCSI_CXGB4_ISCSI
- Reads as
- all on means the file is compiled; any one off means it is not.
From the configuration Debian publishes for every kernel flavour it builds. It covers only the architectures Debian ships a linux-config package for, and nothing about a kernel you built yourself. Debian's own status above stays authoritative about the source package.MAINTAINERS kbuild Makefiles Debian linux-config packages
Signals
- Published
- 2026-08-15 (2 months ago)source
- CVSS
- 9.8 critical
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:Hsource recompute it - Attack vector
- network (AV:N)source
- EPSS
- 0.40%, higher than 32.6% of all CVEssource
- CISA KEV
- not listedthe KEV catalogue
- Debian urgency
- not yet assignedsource
- Subsystem
- drivers/scsi
Upstream fixes
The versions the CNA records as introducing and fixing this, and the commit for each. source
| Introduced | Fixed in | Commit |
|---|---|---|
| 2.6.29 | 5.10.265 | a51812842084 |
| 2.6.29 | 5.15.216 | a8f94cc9f0e5 |
| 2.6.29 | 6.1.183 | f1a3a51fc5db |
| 2.6.29 | 6.6.151 | c97b5265cc47 |
| 2.6.29 | 6.12.103 | 084af0253673 |
| 2.6.29 | 6.18.44 | 72815741715b |
| 2.6.29 | 7.1.8 | b0aa3e8e2ab4 |
| 2.6.29 | 7.2 | c1dea15f819c |
Debian advisories
| Advisory | Date | Shipped to | Debian |
|---|---|---|---|
| DLA-4788-1 | 2026-09-19 | bookworm 6.12.107-1~deb12u1 | tracker |
| DLA-4777-1 | 2026-09-08 | bookworm 6.1.187-1 | tracker |
| DSA-6466-1 | 2026-08-25 | trixie 6.12.105-1 | tracker |
Why the CNA scored it this way
Quoted from the kernel CNA's own scoring file, word for word. A highlighted metric carries the most severe value CVSS v3.1 defines for it, which is what pushes the score up. source
- AV:NAttack vector, network
- A malicious or compromised iSCSI target delivers crafted SCSI Command Response PDUs over the established TCP iSCSI session; reception flows through iscsi_sw_tcp_recv/iscsi_tcp_recv_skb into iscsi_tcp_hdr_dissect without local access.
- AC:LAttack complexity, low
- The attacker controls the target and can set DataSegmentLength between 8193 and negotiated max_recv_dlength (open-iscsi commonly 262144) on SCSI_CMD_RSP for any outstanding command ITT; no races or victim-specific heap layout are required.
- PR:NPrivileges required, none
- No privileges on the victim host are needed; a remote attacker acting as or MITMing the iSCSI target sends malicious responses after session login, independent of victim user accounts or capabilities.
- UI:NUser interaction, none
- On systems with persistent iSCSI sessions (cloud VMs, SAN-boot hosts, Kubernetes iSCSI volumes), exploitation triggers automatically during normal SCSI I/O when command responses are received; no victim action is needed at attack time.
- S:UScope, unchanged
- Heap corruption is confined to the kernel iSCSI initiator on the affected host; successful exploitation yields kernel compromise or DoS within the same security authority, not a VM escape or cross-boundary scope change.
- C:HConfidentiality impact, high
- iscsi_tcp_segment_recv memcpy writes up to max_recv_dlength bytes into an 8192-byte conn->data buffer, causing a large heap overflow whose controlled corruption can be leveraged for arbitrary kernel memory disclosure.
- I:HIntegrity impact, high
- Attacker-controlled response data is copied past the fixed conn->data allocation via iscsi_tcp_data_recv_prep/iscsi_segment_init_linear, enabling heap metadata/object corruption exploitable for arbitrary kernel write and privilege escalation.
- A:HAvailability impact, high
- Overflowing the conn->data heap buffer can immediately corrupt adjacent kernel allocations and cause oops/panic; a malicious target can repeatedly trigger this on active sessions to deny storage availability.