GHSA-VPRC-JRMR-XQ56
Vulnerability from github – Published: 2026-08-15 06:32 – Updated: 2026-08-17 06:33In 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.
{
"affected": [],
"aliases": [
"CVE-2026-72085"
],
"database_specific": {
"cwe_ids": [],
"github_reviewed": false,
"github_reviewed_at": null,
"nvd_published_at": "2026-08-15T06:21:22Z",
"severity": "CRITICAL"
},
"details": "In the Linux kernel, the following vulnerability has been resolved:\n\nscsi: xen: scsiback: Free unsubmitted command instead of double-putting it\n\nscsiback_get_pend_req() obtains a command tag and returns a vscsibk_pend\nwhose embedded se_cmd has only been memset to 0, so its cmd_kref is 0;\nthe se_cmd is initialised (kref_init() via target_init_cmd()) only\nlater, in scsiback_cmd_exec(), on the successful VSCSIIF_ACT_SCSI_CDB\npath. The two error paths in scsiback_do_cmd_fn() taken before the\ncommand is submitted -- a failed scsiback_gnttab_data_map() and an\nunknown ring_req.act -- call\ntransport_generic_free_cmd(\u0026pending_req-\u003ese_cmd, 0), which kref_put()s a\nrefcount of 0. That underflows it (\"refcount_t: underflow;\nuse-after-free\") and, as the release function is not run, leaks the\ncommand tag.\n\nImpact: a pvSCSI guest can leak every command tag of a LUN\u0027s session,\nstopping the LUN, by submitting requests with a bad grant reference or\nan unknown request type; under panic_on_warn the refcount underflow\npanics the host.\n\nAdd a helper that just returns the tag with target_free_tag() and sends\nthe error response. It frees the tag while the v2p reference still pins\nthe session, and snapshots the response fields beforehand because\nfreeing the tag can let another ring reuse the pending_req slot.",
"id": "GHSA-vprc-jrmr-xq56",
"modified": "2026-08-17T06:33:09Z",
"published": "2026-08-15T06:32:11Z",
"references": [
{
"type": "ADVISORY",
"url": "https://nvd.nist.gov/vuln/detail/CVE-2026-72085"
},
{
"type": "WEB",
"url": "https://git.kernel.org/stable/c/1e97c404e44991fb087c38ccd7414f2d326f9b74"
},
{
"type": "WEB",
"url": "https://git.kernel.org/stable/c/9c0f6894982b1f13bda220707497b25ac9c95bdb"
},
{
"type": "WEB",
"url": "https://git.kernel.org/stable/c/a13b789497a7fdd27d4d63f5c69d23db706ef0fe"
},
{
"type": "WEB",
"url": "https://git.kernel.org/stable/c/ca978f8a93d4d36841839bf2847d29b88c2591d6"
},
{
"type": "WEB",
"url": "https://git.kernel.org/stable/c/f1516c56ac540da1769f264c3cfefe4499548a5d"
},
{
"type": "WEB",
"url": "https://git.kernel.org/stable/c/fa588f28401102652068c4cc75e135507f4b5106"
},
{
"type": "WEB",
"url": "https://git.kernel.org/stable/c/fcd64d4d97af5d9736f31040f8ed8cd4c17e4c45"
}
],
"schema_version": "1.4.0",
"severity": [
{
"score": "CVSS:3.1/AV:L/AC:L/PR:N/UI:N/S:C/C:H/I:H/A:H",
"type": "CVSS_V3"
}
]
}
Sightings
| Author | Source | Type | Date | Other |
|---|
Nomenclature
- Seen: The vulnerability was mentioned, discussed, or observed by the user.
- Confirmed: The vulnerability has been validated from an analyst's perspective.
- Published Proof of Concept: A public proof of concept is available for this vulnerability.
- Exploited: The vulnerability was observed as exploited by the user who reported the sighting.
- Patched: The vulnerability was observed as successfully patched by the user who reported the sighting.
- Not exploited: The vulnerability was not observed as exploited by the user who reported the sighting.
- Not confirmed: The user expressed doubt about the validity of the vulnerability.
- Not patched: The vulnerability was not observed as successfully patched by the user who reported the sighting.
The approach is described in our paper Mapping CVEs to MITRE ATT&CK Techniques: A Curated Gold-Set Classifier and the Limits of LLM-Assisted Label Expansion.