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Fencer Vulns
medium 5.5

CVE-2021-26933 json

An issue was discovered in Xen 4.9 through 4.14.x.

published 2021-02-17 5 y ago modified 2026-06-17 4 mo ago also EUVD-2021-13715

cvss
5.5
version 3.1, NVD
cisa kev
Not listed
not in CISA's catalog
epss
0.3%
EPSS 0.3% chance of exploitation in 30 days, percentile 25%
public exploits
0
none known

Summary

An issue was discovered in Xen 4.9 through 4.14.x. On Arm, a guest is allowed to control whether memory accesses are bypassing the cache. This means that Xen needs to ensure that all writes (such as the ones during scrubbing) have reached the memory before handing over the page to a guest. Unfortunately, the operation to clean the cache is happening before checking if the page was scrubbed. Therefore there is no guarantee when all the writes will reach the memory.

Patch / fix

  • xen Debian 14, Debian 13, Debian 12 4.14.1+11-gb0b734a8b3-1

debian advisories DEBIAN-CVE-2021-26933

  • xen Alpine 3.12, Alpine 3.11 4.13.2-r5
  • xen Alpine 3.13 4.14.1-r2
  • xen Alpine 3.24, Alpine 3.23, Alpine 3.22 +8 more 4.14.1-r3

alpine advisories ALPINE-CVE-2021-26933

Alpine secdb © Alpine Linux, from https://secdb.alpinelinux.org via OSV; changed: normalised to fixed package versions per release. CC BY-SA 4.0

Vendor advisories

What the vendors themselves say about their products: affected, fixed or not affected, and what to do.

red hat product security vex CVE-2021-26933 updated

xen: arm: The cache may not be cleaned for newly allocated scrubbed pages

  • Red Hat All currently supported Red Hat products
    not affected: vulnerable code not present

Red Hat CSAF VEX © Red Hat, Inc., from https://security.access.redhat.com/data/csaf/v2/vex/; changed: reduced to product statuses and remediations. CC BY 4.0 · csaf

Exploit prediction

0.33% chance of exploitation in the next 30 days, higher than 25% of all scored CVEs (FIRST EPSS, 2026-11-08).

CVSS scores

assigned by version score vector
NVD 3.1 5.5 CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:N/A:N
NVD 2.0 2.1 AV:L/AC:L/Au:N/C:P/I:N/A:N

References

Sources

Fencer Vulns keeps one entry per vulnerability: the CVE id wins, then GHSA, and records that alias each other are merged, except that two CVEs always keep separate entries. The same data is available as JSON.