CVE-2021-47111 (GCVE-0-2021-47111)

Vulnerability from cvelistv5 – Published: 2024-03-15 20:14 – Updated: 2026-08-05 08:46
VLAI
Title
xen-netback: take a reference to the RX task thread
Summary
In the Linux kernel, the following vulnerability has been resolved: xen-netback: take a reference to the RX task thread Do this in order to prevent the task from being freed if the thread returns (which can be triggered by the frontend) before the call to kthread_stop done as part of the backend tear down. Not taking the reference will lead to a use-after-free in that scenario. Such reference was taken before but dropped as part of the rework done in 2ac061ce97f4. Reintroduce the reference taking and add a comment this time explaining why it's needed. This is XSA-374 / CVE-2021-28691.
Severity
8.8 (High)
CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:C/C:H/I:H/A:H
SSVC
Exploitation: none Automatable: no Technical Impact: partial
CISA Coordinator · CISA-ADP (v2.0.3)
Decision recorded 2024-06-26 20:36 UTC
Assigner
References
Impacted products
Vendor Product Version CPE status
Linux Linux Affected: 2ac061ce97f413bfbbdd768f7d2e0fda2e8170df , < 6b53db8c4c14b4e7256f058d202908b54a7b85b4 (git)
Affected: 2ac061ce97f413bfbbdd768f7d2e0fda2e8170df , < caec9bcaeb1a5f03f2d406305355c853af10c13e (git)
Affected: 2ac061ce97f413bfbbdd768f7d2e0fda2e8170df , < 107866a8eb0b664675a260f1ba0655010fac1e08 (git)
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Linux Linux Affected: 5.5
Unaffected: 0 , < 5.5 (semver)
Unaffected: 5.10.43 , ≤ 5.10.* (semver)
Unaffected: 5.12.10 , ≤ 5.12.* (semver)
Unaffected: 5.13 , ≤ * (original_commit_for_fix)
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    "vulnrichment": {
      "containers": "{\"adp\": [{\"title\": \"CVE Program Container\", \"references\": [{\"url\": \"https://git.kernel.org/stable/c/6b53db8c4c14b4e7256f058d202908b54a7b85b4\", \"tags\": [\"x_transferred\"]}, {\"url\": \"https://git.kernel.org/stable/c/caec9bcaeb1a5f03f2d406305355c853af10c13e\", \"tags\": [\"x_transferred\"]}, {\"url\": \"https://git.kernel.org/stable/c/107866a8eb0b664675a260f1ba0655010fac1e08\", \"tags\": [\"x_transferred\"]}], \"providerMetadata\": {\"orgId\": \"af854a3a-2127-422b-91ae-364da2661108\", \"shortName\": \"CVE\", \"dateUpdated\": \"2024-08-04T05:24:39.854Z\"}}, {\"title\": \"CISA ADP Vulnrichment\", \"metrics\": [{\"other\": {\"type\": \"ssvc\", \"content\": {\"id\": \"CVE-2021-47111\", \"role\": \"CISA Coordinator\", \"options\": [{\"Exploitation\": \"none\"}, {\"Automatable\": \"no\"}, {\"Technical Impact\": \"partial\"}], \"version\": \"2.0.3\", \"timestamp\": \"2024-06-26T20:36:51.215407Z\"}}}], \"providerMetadata\": {\"orgId\": \"134c704f-9b21-4f2e-91b3-4a467353bcc0\", \"shortName\": \"CISA-ADP\", \"dateUpdated\": \"2024-06-26T20:36:55.225Z\"}}], \"cna\": {\"title\": \"xen-netback: take a reference to the RX task thread\", \"metrics\": [{\"cvssV3_1\": {\"version\": \"3.1\", \"baseScore\": 8.8, \"baseSeverity\": \"HIGH\", \"vectorString\": \"CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:C/C:H/I:H/A:H\"}, \"scenarios\": [{\"lang\": \"en\", \"value\": \"AV:L - The attack is carried out by a Xen guest through the PV netfront shared rings and event channels on the same host, not via remote network packets or physical device access.\\nAC:L - The guest reliably triggers the bug by posting a malformed TX request (e.g. excess slots or cross-page offsets) to force the RX kthread to exit, then switching the frontend xenstore state to Closing/Closed to cause backend teardown and the UAF; both steps are fully attacker-controlled.\\nPR:L - Exploitation requires a guest domain with a configured PV network frontend (typical cloud/tenant guest control), which is low privilege relative to Dom0 and does not require host-admin rights.\\nUI:N - No victim user action is required; the guest alone can send the malformed frontend requests and drive the disconnect state change.\\nS:C - This is a Xen guest-to-host escape: a DomU compromises Dom0 kernel memory via UAF in xen-netback, crossing the guest/host security boundary.\\nC:H - Use-after-free of a host task_struct can be leveraged for arbitrary kernel memory disclosure; XSA-374 explicitly states information leaks cannot be ruled out.\\nI:H - The same UAF enables heap reuse and control-flow hijacking in Dom0, and XSA-374 states privilege escalation cannot be ruled out.\\nA:H - Calling kthread_stop() on the freed task_struct can crash or hang Dom0, which XSA-374 confirms as a host denial of service.\"}]}], \"affected\": [{\"repo\": \"https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git\", \"vendor\": \"Linux\", \"product\": \"Linux\", \"versions\": [{\"status\": \"affected\", \"version\": \"2ac061ce97f413bfbbdd768f7d2e0fda2e8170df\", \"lessThan\": \"6b53db8c4c14b4e7256f058d202908b54a7b85b4\", \"versionType\": \"git\"}, {\"status\": \"affected\", \"version\": \"2ac061ce97f413bfbbdd768f7d2e0fda2e8170df\", \"lessThan\": \"caec9bcaeb1a5f03f2d406305355c853af10c13e\", \"versionType\": \"git\"}, {\"status\": \"affected\", \"version\": \"2ac061ce97f413bfbbdd768f7d2e0fda2e8170df\", \"lessThan\": \"107866a8eb0b664675a260f1ba0655010fac1e08\", \"versionType\": \"git\"}], \"programFiles\": [\"drivers/net/xen-netback/interface.c\"], \"defaultStatus\": \"unaffected\"}, {\"repo\": \"https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git\", \"vendor\": \"Linux\", \"product\": \"Linux\", \"versions\": [{\"status\": \"affected\", \"version\": \"5.5\"}, {\"status\": \"unaffected\", \"version\": \"0\", \"lessThan\": \"5.5\", \"versionType\": \"semver\"}, {\"status\": \"unaffected\", \"version\": \"5.10.43\", \"versionType\": \"semver\", \"lessThanOrEqual\": \"5.10.*\"}, {\"status\": \"unaffected\", \"version\": \"5.12.10\", \"versionType\": \"semver\", \"lessThanOrEqual\": \"5.12.*\"}, {\"status\": \"unaffected\", \"version\": \"5.13\", \"versionType\": \"original_commit_for_fix\", \"lessThanOrEqual\": \"*\"}], \"programFiles\": [\"drivers/net/xen-netback/interface.c\"], \"defaultStatus\": \"affected\"}], \"references\": [{\"url\": \"https://git.kernel.org/stable/c/6b53db8c4c14b4e7256f058d202908b54a7b85b4\"}, {\"url\": \"https://git.kernel.org/stable/c/caec9bcaeb1a5f03f2d406305355c853af10c13e\"}, {\"url\": \"https://git.kernel.org/stable/c/107866a8eb0b664675a260f1ba0655010fac1e08\"}], \"x_generator\": {\"engine\": \"bippy-1.2.0\"}, \"descriptions\": [{\"lang\": \"en\", \"value\": \"In the Linux kernel, the following vulnerability has been resolved:\\n\\nxen-netback: take a reference to the RX task thread\\n\\nDo this in order to prevent the task from being freed if the thread\\nreturns (which can be triggered by the frontend) before the call to\\nkthread_stop done as part of the backend tear down. Not taking the\\nreference will lead to a use-after-free in that scenario. Such\\nreference was taken before but dropped as part of the rework done in\\n2ac061ce97f4.\\n\\nReintroduce the reference taking and add a comment this time\\nexplaining why it\u0027s needed.\\n\\nThis is XSA-374 / CVE-2021-28691.\"}], \"cpeApplicability\": [{\"nodes\": [{\"negate\": false, \"cpeMatch\": [{\"criteria\": \"cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*\", \"vulnerable\": true, \"versionEndExcluding\": \"5.10.43\", \"versionStartIncluding\": \"5.5\"}, {\"criteria\": \"cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*\", \"vulnerable\": true, \"versionEndExcluding\": \"5.12.10\", \"versionStartIncluding\": \"5.5\"}, {\"criteria\": \"cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*\", \"vulnerable\": true, \"versionEndExcluding\": \"5.13\", \"versionStartIncluding\": \"5.5\"}], \"operator\": \"OR\"}]}], \"providerMetadata\": {\"orgId\": \"416baaa9-dc9f-4396-8d5f-8c081fb06d67\", \"shortName\": \"Linux\", \"dateUpdated\": \"2026-08-05T08:46:04.618Z\"}}}",
      "cveMetadata": "{\"cveId\": \"CVE-2021-47111\", \"state\": \"PUBLISHED\", \"dateUpdated\": \"2026-08-05T08:46:04.618Z\", \"dateReserved\": \"2024-03-04T18:12:48.836Z\", \"assignerOrgId\": \"416baaa9-dc9f-4396-8d5f-8c081fb06d67\", \"datePublished\": \"2024-03-15T20:14:19.898Z\", \"assignerShortName\": \"Linux\"}",
      "dataType": "CVE_RECORD",
      "dataVersion": "5.2"
    }
  }
}



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Taxonomy of the tags.





Forecast uses a logistic model when the trend is rising, or an exponential decay model when the trend is falling. Fitted via linearized least squares.

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.


Detection rules are retrieved from Rulezet.