Description
In the Linux kernel, the following vulnerability has been resolved:
scsi: xen: scsiback: Free unsubmitted command instead of double-putting it
scsiback_get_pend_req() obtains a command tag and returns a vscsibk_pend
whose embedded se_cmd has only been memset to 0, so its cmd_kref is 0;
the se_cmd is initialised (kref_init() via target_init_cmd()) only
later, in scsiback_cmd_exec(), on the successful VSCSIIF_ACT_SCSI_CDB
path. The two error paths in scsiback_do_cmd_fn() taken before the
command is submitted -- a failed scsiback_gnttab_data_map() and an
unknown ring_req.act -- call
transport_generic_free_cmd(&pending_req->se_cmd, 0), which kref_put()s a
refcount of 0. That underflows it ("refcount_t: underflow;
use-after-free") and, as the release function is not run, leaks the
command tag.
Impact: a pvSCSI guest can leak every command tag of a LUN's session,
stopping the LUN, by submitting requests with a bad grant reference or
an unknown request type; under panic_on_warn the refcount underflow
panics the host.
Add a helper that just returns the tag with target_free_tag() and sends
the error response. It frees the tag while the v2p reference still pins
the session, and snapshots the response fields beforehand because
freeing the tag can let another ring reuse the pending_req slot.
scsi: xen: scsiback: Free unsubmitted command instead of double-putting it
scsiback_get_pend_req() obtains a command tag and returns a vscsibk_pend
whose embedded se_cmd has only been memset to 0, so its cmd_kref is 0;
the se_cmd is initialised (kref_init() via target_init_cmd()) only
later, in scsiback_cmd_exec(), on the successful VSCSIIF_ACT_SCSI_CDB
path. The two error paths in scsiback_do_cmd_fn() taken before the
command is submitted -- a failed scsiback_gnttab_data_map() and an
unknown ring_req.act -- call
transport_generic_free_cmd(&pending_req->se_cmd, 0), which kref_put()s a
refcount of 0. That underflows it ("refcount_t: underflow;
use-after-free") and, as the release function is not run, leaks the
command tag.
Impact: a pvSCSI guest can leak every command tag of a LUN's session,
stopping the LUN, by submitting requests with a bad grant reference or
an unknown request type; under panic_on_warn the refcount underflow
panics the host.
Add a helper that just returns the tag with target_free_tag() and sends
the error response. It frees the tag while the v2p reference still pins
the session, and snapshots the response fields beforehand because
freeing the tag can let another ring reuse the pending_req slot.
Published:
2026-08-15
Score:
n/a
EPSS:
< 1% Very Low
KEV:
No
Impact:
n/a
Action:
n/a
Analysis
Analysis and contextual insights are available on OpenCVE Cloud.
Default status is the baseline for the product, each version can override it (e.g. patched versions marked unaffected).
| Vendor | Product | Default status | Versions | ||||||||||||||||||||||||||||||
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
| Linux | Linux | unaffected |
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| Linux | Linux | affected |
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No data.
No data.
| Vendor | Product | Confidence | Versions | ||||||||||||||||||||||||||||||||||||||||
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
| Linux | Linux Kernel | 99% |
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| Linux | Linux Kernel | 99% |
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Remediation
No vendor fix or workaround currently provided.
Additional remediation guidance may be available on OpenCVE Cloud.
Tracking
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Advisories
No advisories yet.
References
History
Sat, 15 Aug 2026 06:00:00 +0000
| Type | Values Removed | Values Added |
|---|---|---|
| Description | In the Linux kernel, the following vulnerability has been resolved: scsi: xen: scsiback: Free unsubmitted command instead of double-putting it scsiback_get_pend_req() obtains a command tag and returns a vscsibk_pend whose embedded se_cmd has only been memset to 0, so its cmd_kref is 0; the se_cmd is initialised (kref_init() via target_init_cmd()) only later, in scsiback_cmd_exec(), on the successful VSCSIIF_ACT_SCSI_CDB path. The two error paths in scsiback_do_cmd_fn() taken before the command is submitted -- a failed scsiback_gnttab_data_map() and an unknown ring_req.act -- call transport_generic_free_cmd(&pending_req->se_cmd, 0), which kref_put()s a refcount of 0. That underflows it ("refcount_t: underflow; use-after-free") and, as the release function is not run, leaks the command tag. Impact: a pvSCSI guest can leak every command tag of a LUN's session, stopping the LUN, by submitting requests with a bad grant reference or an unknown request type; under panic_on_warn the refcount underflow panics the host. Add a helper that just returns the tag with target_free_tag() and sends the error response. It frees the tag while the v2p reference still pins the session, and snapshots the response fields beforehand because freeing the tag can let another ring reuse the pending_req slot. | |
| Title | scsi: xen: scsiback: Free unsubmitted command instead of double-putting it | |
| First Time appeared |
Linux
Linux linux Kernel |
|
| CPEs | cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:* | |
| Vendors & Products |
Linux
Linux linux Kernel |
|
| References |
|
|
MITRE
Status: PUBLISHED
Assigner: Linux
Published:
Updated: 2026-08-15T05:52:33.521Z
Reserved: 2026-08-09T03:40:39.904Z
Link: CVE-2026-72085
Vulnrichment
No data.
NVD
Status : Received
Published: 2026-08-15T06:21:22.470
Modified: 2026-08-15T06:21:22.470
Link: CVE-2026-72085
Redhat
No data.
OpenCVE Enrichment
Updated: 2026-08-15T12:45:06Z
Weaknesses
No weakness.