{ "dataType": "CVE_RECORD", "dataVersion": "5.2", "cveMetadata": { "cveId": "CVE-2026-68173", "assignerOrgId": "416baaa9-dc9f-4396-8d5f-8c081fb06d67", "state": "PUBLISHED", "assignerShortName": "Linux", "dateReserved": "2026-07-30T09:28:09.372Z", "datePublished": "2026-08-10T11:59:42.889Z", "dateUpdated": "2026-08-17T05:00:14.047Z" }, "containers": { "cna": { "providerMetadata": { "orgId": "416baaa9-dc9f-4396-8d5f-8c081fb06d67", "shortName": "Linux", "dateUpdated": "2026-08-17T05:00:14.047Z" }, "descriptions": [ { "lang": "en", "value": "In the Linux kernel, the following vulnerability has been resolved:\n\nublk: wait on ublk_dev_ready() instead of ub->completion\n\nub->completion is only re-armed by a successful START_USER_RECOVERY. If\nthe ublk server sends END_USER_RECOVERY without one - e.g. its START\nfailed with -EBUSY and the error was ignored - the wait is satisfied by\nthe stale completion of the previous recovery cycle, and the device is\nmarked LIVE and the requeue list kicked while the FETCH stream is still\nrunning and ubq->canceling is still set. The kick redispatches a\npreviously requeued request, __ublk_queue_rq_common() sees ->canceling\nand parks it again via __ublk_abort_rq(), and after the last FETCH\nclears ->canceling nothing ever kicks the requeue list again: the\nrequest is stranded there while holding its tag. If it is the flush\nmachinery's flush_rq, every subsequent fsync piles up in uninterruptible\nsleep and teardown hangs on tag draining. This matches a report of a\nlost PREFLUSH with ext4 on top of ublk after daemon crash recovery.\n\nub->completion is an edge-triggered latch used as a proxy for the level\ncondition \"every queue has fetched all I/O commands\", which can regress\n(F_BATCH's UNPREP, daemon death) and whose re-arm can be skipped. Drop\nit and wait on the real condition instead: the new helper\nublk_wait_dev_ready_and_lock() waits on ublk_dev_ready() via\nwait_var_event_interruptible(), woken from ublk_mark_io_ready(), then\nre-checks it under ub->mutex, waiting again on regression, and returns\nwith the mutex held and readiness guaranteed.\n\nReadiness becomes true in the same ub->mutex critical section that\nclears the last queue's ->canceling, so END_USER_RECOVERY marks the\ndevice LIVE and kicks the requeue list strictly after ->canceling\nclears. The wait stays interruptible, so a server whose daemon died can\nstill be signalled out. For ublk_ctrl_start_dev() this replaces the\nfail-fast -EINVAL on an F_BATCH ready->UNPREP regression with waiting\nuntil the device is ready again." } ], "metrics": [ { "cvssV3_1": { "version": "3.1", "vectorString": "CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:H/A:H", "baseScore": 7.1, "baseSeverity": "HIGH" }, "scenarios": [ { "lang": "en", "value": "AV:L - The bug is reached only via io_uring commands (UBLK_CMD_END_USER_RECOVERY/UBLK_CMD_START_DEV) on /dev/ublk-control or ublk char devices; there is no network, Bluetooth, or physical-bus entry path to the vulnerable wait/completion logic.\nAC:L - An actor controlling the ublk server can reliably trigger stale-completion early wakeup by calling END_USER_RECOVERY after START_USER_RECOVERY failed (e.g., -EBUSY) without re-arming completion; the attacker controls both sides of the recovery sequence and needs no uncontrollable timing.\nPR:L - Recovery requires UBLK_F_USER_RECOVERY devices managed through ublk-control, which needs CAP_SYS_ADMIN for privileged devices; per kernel CNA guidance, CAP_SYS_ADMIN obtainable in a user namespace (unshare -Urn) counts as Low, not High.\nUI:N - Exploitation is driven by the ublk daemon issuing recovery/start control commands during crash recovery or restart; no end-user action such as opening files, mounting media, or clicking prompts is required.\nS:U - Impact is confined to the kernel block/ublk stack and filesystems backed by the affected ublk device; it does not cross VM, container, or IOMMU boundaries into a separate security authority.\nC:N - This is a state-machine/completion synchronization flaw, not memory corruption; it strands block requests and breaks flush barriers but does not read or disclose kernel or user memory.\nI:H - Premature END_USER_RECOVERY can strand the block layer flush_rq and lose PREFLUSH ordering (reported with ext4), breaking durability guarantees and allowing arbitrary user data loss or corruption after crash or power loss.\nA:H - Stranded flush_rq holds its MQ tag indefinitely, causing every subsequent fsync to sleep uninterruptibly (D state) and device teardown to hang on tag draining, producing a persistent kernel-level denial of service on the backing block device." } ] } ], "affected": [ { "product": "Linux", "vendor": "Linux", "defaultStatus": "unaffected", "repo": "https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git", "programFiles": [ "drivers/block/ublk_drv.c" ], "versions": [ { "version": "728cbac5fe219d3b8a21a0688a08f2b7f8aeda2b", "lessThan": "7dd26adf7e7d482af524e3a0cca4a81ef7c159d0", "status": "affected", "versionType": "git" }, { "version": "728cbac5fe219d3b8a21a0688a08f2b7f8aeda2b", "lessThan": "8f188dd11a1c2ad94caeaee36ef68bb8221d4a12", "status": "affected", "versionType": "git" }, { "version": "728cbac5fe219d3b8a21a0688a08f2b7f8aeda2b", "lessThan": "432a9b2780c0a01caf547bd1fc2fcf28aeb8d173", "status": "affected", "versionType": "git" }, { "version": "42ea64e01c96e594fb4f80c54dfe4f934d008a6e", "status": "affected", "versionType": "git" }, { "version": "6.14.6", "lessThan": "6.15", "status": "affected", "versionType": "semver" } ] }, { "product": "Linux", "vendor": "Linux", "defaultStatus": "affected", "repo": "https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git", "programFiles": [ "drivers/block/ublk_drv.c" ], "versions": [ { "version": "6.15", "status": "affected" }, { "version": "0", "lessThan": "6.15", "status": "unaffected", "versionType": "semver" }, { "version": "6.18.42", "lessThanOrEqual": "6.18.*", "status": "unaffected", "versionType": "semver" }, { "version": "7.1.6", "lessThanOrEqual": "7.1.*", "status": "unaffected", "versionType": "semver" }, { "version": "7.2", "lessThanOrEqual": "*", "status": "unaffected", "versionType": "original_commit_for_fix" } ] } ], "cpeApplicability": [ { "nodes": [ { "operator": "OR", "negate": false, "cpeMatch": [ { "vulnerable": true, "criteria": "cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*", "versionStartIncluding": "6.15", "versionEndExcluding": "6.18.42" }, { "vulnerable": true, "criteria": "cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*", "versionStartIncluding": "6.15", "versionEndExcluding": "7.1.6" }, { "vulnerable": true, "criteria": "cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*", "versionStartIncluding": "6.15", "versionEndExcluding": "7.2" }, { "vulnerable": true, "criteria": "cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*", "versionStartIncluding": "6.14.6" } ] } ] } ], "references": [ { "url": "https://git.kernel.org/stable/c/7dd26adf7e7d482af524e3a0cca4a81ef7c159d0" }, { "url": "https://git.kernel.org/stable/c/8f188dd11a1c2ad94caeaee36ef68bb8221d4a12" }, { "url": "https://git.kernel.org/stable/c/432a9b2780c0a01caf547bd1fc2fcf28aeb8d173" } ], "title": "ublk: wait on ublk_dev_ready() instead of ub->completion", "x_generator": { "engine": "bippy-1.2.0" } } } }