Medium [CVE-2026-64027] rework the VALID marking (again)
This medium-severity Red Hat Linux advisory covers CVE-2026-64027 affecting Red Hat Enterprise Linux 10, Shadow Migration Toolkit for Virtualization for RHEL 10, Red Hat Enterprise Linux 9.
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Summary
In the Linux kernel, the following vulnerability has been resolved: net: shaper: rework the VALID marking (again) Recent commit changed the semantics from NOT_VALID to VALID. I didn't realize that the flags are not stored atomically with the entry in XArray.
There's still a race of reader observing a VALID mark for a slot, getting interrupted, writer replacing the entry with a different one, reader continuing, fetching the entry which is now a different pointer than the pointer for which VALID was meant.
The biggest consequence of this is that we may see a UAF since net_shaper_rollback() assumed that entries without VALID can be freed without observing RCU. Looks like the XArray marks are buying us nothing at this point.
Let's convert the code to an explicit valid field. The smp_load_acquire() / smp_store_release() barriers are marginally cleaner.
A race condition exists in how `VALID` marks are handled for entries in an XArray. This can lead to a Use-After-Free (UAF) vulnerability, where memory is incorrectly freed while still in use, potentially allowing an attacker to cause a denial of service or execute arbitrary code.
Red Hat severity: Moderate — CVSS 4.7 (CVSS:3.1/AV:L/AC:H/PR:L/UI:N/S:U/C:N/I:N/A:H). Weakness: CWE-367.
Affected Red Hat products: Red Hat Enterprise Linux 10; Shadow Migration Toolkit for Virtualization for RHEL 10; Red Hat Enterprise Linux 9.
Affected versions
No affected-version range was extracted from the source record. The vendor advisory is authoritative. Check it before change work.
Official advisory · high-confidence parse· fetched 7 days ago·verify at source
- kernel-0:6.12.0-211.69.1.el10_2
- RHSA-2026:91565
Official advisory · high-confidence parse· fetched 7 days ago·verify at source
Mitigation
Upgrade to a fixed release: kernel-0:6.12.0-211.69.1.el10_2, RHSA-2026:91565. That is the remediation for this advisory.
The vendor advisory may list interim mitigations or workarounds not captured here. Review it before change work.
Official advisory · high-confidence parse· fetched 7 days ago·verify at source
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