CVE-2026-89968: nvmet-tcp: reject unsolicited H2CData PDUs
In the Linux kernel, the following vulnerability has been resolved:
nvmet-tcp: reject unsolicited H2CData PDUs
nvmettcphandleh2cdatapdu() accepts an H2CData PDU after only checking that its TTAG is a valid in-range command index and that the command's data buffers are mapped. It never checks that the target has actually solicited that data by sending an R2T for the command.
A remote host can abuse this. It submits a write command that takes the R2T path and, before the target transmits the R2T, sends an H2CData PDU for that command's tag. The data completes the command early, and when the command then fails synchronously (e.g. a length mismatch caught by nvmetchecktransferlen()), it is completed a second time. Each completion calls nvmettcpqueueresponse(), so the same command is added to queue->resplist twice while it is still linked; the second llistadd() makes the node point to itself (lentry->next == lentry).
nvmettcpprocessresplist() then walks that self-referential node and adds the command to respsendlist twice. With CONFIGDEBUGLIST this trips the "listadd double add" check (kernel BUG); without it the loop never terminates and the nvmettcp workqueue wedges (soft-lockup). It is remotely triggerable and needs no authentication on an allowanyhost subsystem.
Track whether an R2T has been transmitted for a command and reject an H2CData PDU that arrives before it. The flag is cleared on command reuse (nvmettcpgetcmd() zeroes cmd->flags) and stays set across the multiple H2CData PDUs of a single solicited transfer.
Affected Software
Remediation
Recommended actions to resolve this vulnerability, in priority order.
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Fixed in 6.6.157.1-1 - Upgrade
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debian/linuxto a version that resolves this vulnerability.Fixed in 6.1.190-1Fixed in 6.12.115-2Fixed in 7.2.12-1Fixed in 7.2.15-1 - Upgrade
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debian/linux-6.12to a version that resolves this vulnerability.Fixed in 6.12.113-1~deb12u1 - Upgrade
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ubuntu/linux-aws-5.15to a version that resolves this vulnerability.Fixed in 5.15.0-1119.126~20.04.1 - Upgrade
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ubuntu/linux-nvidia-tegra-5.15to a version that resolves this vulnerability.Fixed in 5.15.0-1070.72~20.04.1 - Upgrade
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ubuntu/linuxto a version that resolves this vulnerability.Fixed in 5.15.0-202.212 - Upgrade
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ubuntu/linux-awsto a version that resolves this vulnerability.Fixed in 5.15.0-1119.126 - Upgrade
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ubuntu/linux-azureto a version that resolves this vulnerability.Fixed in 5.15.0-1125.134 - Upgrade
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ubuntu/linux-lowlatencyto a version that resolves this vulnerability.Fixed in 5.15.0-197.207 - Upgrade
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ubuntu/linux-fipsto a version that resolves this vulnerability.Fixed in 5.15.0-202.212+fips1 - Upgrade
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ubuntu/linux-gcp-fipsto a version that resolves this vulnerability.Fixed in 5.15.0-1120.130+fips1 - Upgrade
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ubuntu/linux-hwe-7.0to a version that resolves this vulnerability.Fixed in 7.0.0-42.42~24.04.1 - Upgrade
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ubuntu/linux-riscv-7.0to a version that resolves this vulnerability.Fixed in 7.0.0-42.42.1~24.04.1 - Upgrade
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ubuntu/linuxto a version that resolves this vulnerability.Fixed in 7.0.0-42.42 - Upgrade
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ubuntu/linux-awsto a version that resolves this vulnerability.Fixed in 7.0.0-1016.17 - Upgrade
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ubuntu/linux-gcpto a version that resolves this vulnerability.Fixed in 7.0.0-1016.18 - Upgrade
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ubuntu/linux-ibmto a version that resolves this vulnerability.Fixed in 7.0.0-1017.17 - Upgrade
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ubuntu/linux-oem-7.0to a version that resolves this vulnerability.Fixed in 7.0.0-1017.17 - Upgrade
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ubuntu/linux-oracleto a version that resolves this vulnerability.Fixed in 7.0.0-1015.16 - Upgrade
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ubuntu/linux-riscvto a version that resolves this vulnerability.Fixed in 7.0.0-42.42.1 - Compensating control
In nvmet_tcp_handle_h2c_data_pdu(), track whether an R2T has been transmitted for the command and reject any H2CData PDU that arrives before the R2T.
Event History
Frequently Asked Questions
Which systems are exposed to this issue?
Linux kernel systems using the nvmet-tcp target functionality are exposed to a remote host that can submit NVMe/TCP write commands to the target.
What does an attacker need to do to trigger the flaw?
The attacker submits a write command that takes the R2T path, then sends an H2CData PDU for that command before the target has transmitted the corresponding R2T. The vulnerable handler accepts the unsolicited data when the command tag is in range and its data buffers are mapped.
What is the operational impact?
The command can be completed twice and added to response lists multiple times. With CONFIG_DEBUG_LIST enabled, this triggers a kernel BUG; without it, response-list processing can loop indefinitely and prevent the nvmet-tcp workqueue from making progress.