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CVE Record

CVE-2026-43249: 9p/xen: protect xen_9pfs_front_free against concurrent calls

In the Linux kernel, the following vulnerability has been resolved: 9p/xen: protect xen_9pfs_front_free against concurrent calls The xenwatch thread can race with other back-end change notifications and call xen_9pfs_front_free() twice, hitting the observed general protection fault due to a double-free. Guard the teardown path so only one caller can release the front-end state at a time, preventing the crash. This is a fix for the following double-free: [ 27.052347] Oops: general protection fault, probably for non-canonical address 0x6b6b6b6b6b6b6b6b: 0000 [#1] SMP DEBUG_PAGEALLOC NOPTI [ 27.052357] CPU: 0 UID: 0 PID: 32 Comm: xenwatch Not tainted 6.18.0-02087-g51ab33fc0a8b-dirty #60 PREEMPT(none) [ 27.052363] RIP: e030:xen_9pfs_front_free+0x1d/0x150 [ 27.052368] Code: 90 90 90 90 90 90 90 90 90 90 90 90 90 41 55 41 54 55 48 89 fd 48 c7 c7 48 d0 92 85 53 e8 cb cb 05 00 48 8b 45 08 48 8b 55 00 <48> 3b 28 0f 85 f9 28 35 fe 48 3b 6a 08 0f 85 ef 28 35 fe 48 89 42 [ 27.052377] RSP: e02b:ffffc9004016fdd0 EFLAGS: 00010246 [ 27.052381] RAX: 6b6b6b6b6b6b6b6b RBX: ffff88800d66e400 RCX: 0000000000000000 [ 27.052385] RDX: 6b6b6b6b6b6b6b6b RSI: 0000000000000000 RDI: 0000000000000000 [ 27.052389] RBP: ffff88800a887040 R08: 0000000000000000 R09: 0000000000000000 [ 27.052393] R10: 0000000000000000 R11: 0000000000000000 R12: ffff888009e46b68 [ 27.052397] R13: 0000000000000200 R14: 0000000000000000 R15: ffff88800a887040 [ 27.052404] FS: 0000000000000000(0000) GS:ffff88808ca57000(0000) knlGS:0000000000000000 [ 27.052408] CS: e030 DS: 0000 ES: 0000 CR0: 0000000080050033 [ 27.052412] CR2: 00007f9714004360 CR3: 0000000004834000 CR4: 0000000000050660 [ 27.052418] Call Trace: [ 27.052420] <TASK> [ 27.052422] xen_9pfs_front_changed+0x5d5/0x720 [ 27.052426] ? xenbus_otherend_changed+0x72/0x140 [ 27.052430] ? __pfx_xenwatch_thread+0x10/0x10 [ 27.052434] xenwatch_thread+0x94/0x1c0 [ 27.052438] ? __pfx_autoremove_wake_function+0x10/0x10 [ 27.052442] kthread+0xf8/0x240 [ 27.052445] ? __pfx_kthread+0x10/0x10 [ 27.052449] ? __pfx_kthread+0x10/0x10 [ 27.052452] ret_from_fork+0x16b/0x1a0 [ 27.052456] ? __pfx_kthread+0x10/0x10 [ 27.052459] ret_from_fork_asm+0x1a/0x30 [ 27.052463] </TASK> [ 27.052465] Modules linked in: [ 27.052471] ---[ end trace 0000000000000000 ]---

HighCVSS 8.8Not KEV-listedUpdated
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Glexia's TakeAutomated analysishigh

Security readout for executives and security teams

Plain-English summary

A race condition in Linux’s Xen 9p filesystem front end can make two kernel paths free the same state, causing a kernel fault and system crash. Exposure appears limited to affected Linux systems using Xen with the 9p front end. The supplied evidence demonstrates a crash, but not successful data theft, code execution, or active exploitation.

Executive priority

Treat this as a high-priority reliability and isolation risk for Xen environments using 9p, especially important workloads where a guest crash is costly. Scope first because exposure is configuration-dependent. Patch confirmed users through supported kernel channels promptly; broad emergency action across Linux systems without Xen 9p is not supported by the supplied evidence.

Technical view

Concurrent Xen backend-change notifications can invoke xen_9pfs_front_free() twice. The resulting double-free produced a general protection fault in the xenwatch thread. The kernel fix serializes teardown so only one caller releases front-end state. CVSS 3.1 is 8.8 with adjacent access and high confidentiality, integrity, and availability impacts, although the supplied trace only confirms a crash.

Likely exposure

Prioritize Linux guests running an affected kernel under Xen where the Xen 9p filesystem front end is enabled or used. Systems not using Xen 9p are unlikely to reach the vulnerable path. The supplied version data mixes release numbers and commit identifiers, so distribution-specific exposure must be confirmed against vendor guidance and the referenced fixes.

Exploitation context

The CVE is not listed as KEV in the supplied bundle, and no source provided claims active exploitation or a public exploit. Exploitation would require reaching the Xen 9p backend-notification race from an adjacent context. The evidence establishes a double-free and kernel crash; it does not establish reliable privilege escalation, code execution, or information disclosure.

Researcher notes

The demonstrated failure is a teardown race causing a second free and general protection fault. The fix guards xen_9pfs_front_free() against concurrent callers. CVSS implies broader security impact, but the bundle contains no proof of a controllable memory-corruption primitive. Version interpretation requires care because the affected data includes unusual entries such as “0” and “7.0.”

Mitigation direction

  • Install a vendor-supported kernel containing the applicable referenced stable fix.
  • Prioritize Xen guests that actively use the Xen 9p filesystem front end.
  • If patching is delayed, consult vendor guidance about safely disabling unused Xen 9p functionality.
  • Avoid assuming upstream release numbers map directly to distribution kernel package versions.

Validation and detection

  • Inventory Linux kernel versions on Xen guests and identify active Xen 9p usage.
  • Compare vendor kernel packages with advisories and the referenced stable fix commits.
  • Confirm the updated kernel is running after installation and any required reboot.
  • Monitor affected systems for xenwatch faults, kernel oopses, or unexpected guest crashes.
Prepared
Confidence
high
Sources
6

Public sources used

Generated from the cited source records. This long-tail analysis has not been individually reviewed by a named human.

Potential ATT&CK relevance

Conservative CVE-to-ATT&CK context

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CVE-2026-43249 mapping review

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Vulnerability profileCVE Program record
Severity
High
CVSS
8.8 (3.1)
Known Exploited
No
Published

Vector: CVSS:3.1/AV:A/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H

Official CVE source material

CNA and ADP enrichment extracted from CVE v5

These fields come from the CVE record and ADP containers, not from Glexia's Take. They preserve time-varying source decisions such as CISA SSVC, KEV status, CVSS metrics, and provider references.

1CVSS vectors
3Timeline events
0ADP providers
5Source links

CVSS vector scores

1 official score

We collect every scored CVSS vector available in the official CNA and ADP containers. When more than one version is present, the table keeps the source vectors side by side instead of collapsing them into the highest score.

ScoreVersionSeverityVectorExploitImpactSource
8.8CVSS 3.1HighCVSS:3.1/AV:A/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H2.85.9Linux

Vulnerability scoring details

Base CVSS 3.1 score

8.8High
CVSS 3.1 vector shape for CVE-2026-43249Attack VectorAttack ComplexityPrivileges RequiredUser InteractionScopeConfidentiality ImpactIntegrity ImpactAvailability Impact

Vector: CVSS:3.1/AV:A/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H

Attack Vector
NetworkAdjacentLocalPhysical
Attack Complexity
LowHigh
Privileges Required
NoneLowHigh
User Interaction
NoneRequired
Scope
ChangedUnchanged
Confidentiality Impact
HighLowNone
Integrity Impact
HighLowNone
Availability Impact
HighLowNone

Vulnerability timeline

Timeline events are normalized from CVE metadata, CNA source timelines, ADP timelines, and KEV metadata when present.

  1. CVE reservedCVE Program

    The CVE ID was reserved by the assigning CNA.

  2. CVE publishedCVE Program

    The CVE record was published.

  3. CVE updatedCVE Program

    The CVE record metadata indicates this as the latest update time.

Source materials

Affected products

Products and packages named in the record

VendorProductVersion / packageStatus
LinuxLinuxc15fe55d14b3b4ded5af2a3260877460a6ffb8ad, c15fe55d14b3b4ded5af2a3260877460a6ffb8ad, c15fe55d14b3b4ded5af2a3260877460a6ffb8ad, c15fe55d14b3b4ded5af2a3260877460a6ffb8ad, be03c4fe72384366fd4077a70966bd3b8fc49013, 1ab4de11232e83b875b071aa44d1155634ca8a1e, 7cc9dbae8a5f73bd555130384ea256018d28f283, 3e0359f151ac151abe3fa71040e450ed69cb824b, 8d3fc907d060c4fb33203e616a395a22083b6566, 4f0e9244770f5b75a16d8c0929063cd336926764, 5f6a8974e9ef317fe63f88bab1f33070195dd147, 4.14.308, 4.19.276, 5.4.235, 5.10.173, 5.15.100, 6.1.18, 6.2.5unaffected
LinuxLinux6.3, 0, 6.12.75, 6.18.16, 6.19.6, 7.0affected
Weakness

CWE details

No CWE listed

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