CVE intelligence and bounded remediation

CVE-2021-20181 — A race condition flaw was found in the 9pfs server implementation of QEMU up to and including 5.2.0

High CVSS 7.5

A race condition flaw was found in the 9pfs server implementation of QEMU up to and including 5.2.0. This flaw allows a malicious 9p client to cause a use-after-free error, potentially escalating their privileges on the system. The highest threat from this vulnerability is to confidentiality, integrity as well as system availability.

Severity
High
CVSS
7.5 (3.1)
Published
2021-05-13
CISA KEV
Not currently listed
Ecosystem
software/application
Weaknesses
CWE-367, CWE-362

Affected products

  • qemu / qemu
  • debian / debian_linux / 9.0
  • debian / debian_linux / 10.0

Matched remediation archetype

Race condition, TOCTOU, and lifecycle synchronization

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Check exposure

  • Map concurrent actors, shared state, lock boundaries, signals, callbacks, retries, and check-then-use sequences in the affected path.
  • Determine whether untrusted users can influence timing, object names, filesystem state, or repeated state transitions.
  • Identify clustered and multi-process behavior that repository-local tests may not represent.

Remediate safely

  • Make the sensitive state transition atomic or protect it with a consistently ordered synchronization primitive.
  • Perform authorization and invariant checks on the same authoritative object and transaction used for the operation.
  • Use unique private resources, safe ownership transfer, and idempotent operations; add deterministic concurrency regression tests.

Authoritative sources

Complete CVE record and remediation plan

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