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CVE-2021-26933

An issue was discovered in Xen 4.9 through 4.14.x. On Arm, a guest is allowed to control whether...

5.5 MediumFix available

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.

Attack profile

How easy it is to exploit

Attack vector
Local
Complexity
Low
Privileges needed
Low
User interaction
None

What an attacker can affect

Confidentiality
High
Integrity
None
Availability
None

Exploit likelihood

0.33%Down 0.7 points since Apr 14, 2021
90%50%10%1%

What each source reports

NVD Score used5.5

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.

Record
CVE-2021-26933
CVSS 3.1
5.5 MediumCVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:N/A:N
CVSS 2.0
2.1 LowAV:L/AC:L/Au:N/C:P/I:N/A:N
Updated
2026-11-02
CVE ListNo score

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.

Record
CVE-2021-26933
Updated
2026-11-02
EUVDEUVD-2021-13715No score

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.

Record
EUVD-2021-13715
Updated
2026-11-03
GitHub AdvisoriesGHSA-3c29-qfhr-mp785.5

An issue was discovered in Xen 4.9 through 4.14.x. On Arm, a guest is allowed to control whether...

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.

Record
GHSA-3c29-qfhr-mp78
CVSS 3.1
5.5 MediumCVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:N/A:N
Updated
2026-11-02
OSVALPINE-CVE-2021-269335.5

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.

Record
ALPINE-CVE-2021-26933
CVSS 3.1
5.5 MediumCVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:N/A:N
Updated
2026-11-02
OSV5.5

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.

Record
CVE-2021-26933
CVSS 3.1
5.5 MediumCVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:N/A:N
Updated
2026-11-02
OSVDEBIAN-CVE-2021-269335.5

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.

Record
DEBIAN-CVE-2021-26933
CVSS 3.1
5.5 MediumCVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:N/A:N
Updated
2026-11-02
OSVUBUNTU-CVE-2021-269335.5

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.

Record
UBUNTU-CVE-2021-26933
CVSS 3.1
5.5 MediumCVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:N/A:N
Updated
2026-11-02

Affected products

Affected packages

Affected packages
PackageAffectedFixed
xen
Alpine:v3.11
4.9.0 up to 4.13.2-r5
4.13.2-r5
xen
Alpine:v3.12
4.9.0 up to 4.13.2-r5
4.13.2-r5
xen
Alpine:v3.13
4.9.0 up to 4.14.1-r2
4.14.1-r2
xen
Alpine:v3.14
4.9.0 up to 4.14.1-r3
4.14.1-r3
xen
Alpine:v3.15
4.9.0 up to 4.14.1-r3
4.14.1-r3
xen
Alpine:v3.16
4.9.0 up to 4.14.1-r3
4.14.1-r3
xen
Alpine:v3.17
4.9.0 up to 4.14.1-r3
4.14.1-r3
xen
Alpine:v3.18
4.9.0 up to 4.14.1-r3
4.14.1-r3
xen
Alpine:v3.19
4.9.0 up to 4.14.1-r3
4.14.1-r3
xen
Alpine:v3.20
4.9.0 up to 4.14.1-r3
4.14.1-r3
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Affected packages
PackageAffectedFixed
xen
Alpine:v3.21
4.9.0 up to 4.14.1-r3
4.14.1-r3
xen
Alpine:v3.22
4.9.0 up to 4.14.1-r3
4.14.1-r3
xen
Alpine:v3.23
4.9.0 up to 4.14.1-r3
4.14.1-r3
xen
Alpine:v3.24
4.9.0 up to 4.14.1-r3
4.14.1-r3
xen
Debian:12
before 4.14.1+11-gb0b734a8b3-1
4.14.1+11-gb0b734a8b3-1
xen
Debian:13
before 4.14.1+11-gb0b734a8b3-1
4.14.1+11-gb0b734a8b3-1
xen
Debian:14
before 4.14.1+11-gb0b734a8b3-1
4.14.1+11-gb0b734a8b3-1
xen
Debian:10
From an advisory covering 2 CVEs
before 4.11.4+99-g8bce4698f6-1, plus listed versions
4.11.1+92-g6c33308a8d-24.11.3+24-g14b62ab3e5-14.11.3+24-g14b62ab3e5-1~deb10u14.11.4+24-gddaaccbbab-14.11.4+24-gddaaccbbab-1~deb10u1
Show 4 moreShow less
4.11.4+37-g3263f257ca-14.11.4+57-g41a822c392-14.11.4+57-g41a822c392-24.11.4-1
4.11.4+99-g8bce4698f6-1
xen
Ubuntu:16.04:LTS
All versions, plus listed versions
4.5.1-0ubuntu14.5.1-0ubuntu24.6.0-1ubuntu14.6.0-1ubuntu24.6.0-1ubuntu4
Show 7 moreShow less
4.6.0-1ubuntu4.14.6.0-1ubuntu4.24.6.0-1ubuntu4.34.6.5-0ubuntu14.6.5-0ubuntu1.14.6.5-0ubuntu1.24.6.5-0ubuntu1.4
None known
xen
Ubuntu:18.04:LTS
All versions, plus listed versions
4.9.0-0ubuntu34.9.0-0ubuntu44.9.2-0ubuntu1
None known
xen
Ubuntu:20.04:LTS
All versions, plus listed versions
4.9.2-0ubuntu24.9.2-0ubuntu64.9.2-0ubuntu74.11.3+24-g14b62ab3e5-1ubuntu14.11.3+24-g14b62ab3e5-1ubuntu24.11.3+24-g14b62ab3e5-1ubuntu2.24.11.3+24-g14b62ab3e5-1ubuntu2.3
None known
xen
Ubuntu:22.04:LTS
All versions, plus listed versions
4.11.4+24-gddaaccbbab-1ubuntu24.16.0-1~ubuntu24.16.0-1~ubuntu2.1
None known
xen
Ubuntu:24.04:LTS
All versions, plus listed versions
4.17.2-14.17.2+55-g0b56bed864-14.17.2+76-ge1f9cb16e2-14.17.2+76-ge1f9cb16e2-1ubuntu14.17.3+10-g091466ba55-14.17.3+10-g091466ba55-1.1ubuntu24.17.3+10-g091466ba55-1.1ubuntu3
None known
xen
Ubuntu:25.10
All versions, plus listed versions
4.20.0-1ubuntu14.20.0+68-g35cb38b222-1
None known
xen
Ubuntu:26.10
All versions, plus listed versions
4.20.2+7-g1badcf5035-2build24.20.2+37-g61ff35323e-1ubuntu14.20.3+127-gc42374a105-1
None known
xen
Ubuntu:26.04:LTS
All versions, plus listed versions
4.20.0+68-g35cb38b222-14.20.2+7-g1badcf5035-24.20.2+7-g1badcf5035-2build2
None known

History

History
RecordedChangedSources
affected, facts
aliasesEUVD
first indexedCVE List, GitHub Advisories, NVD, OSV

Dates are when Every CVE recorded each change. Upstream dates may differ.

In short

CVE-2021-26933 is a medium vulnerability (CVSS 5.5) in Xen, published February 17, 2021. No source lists public exploit code. EPSS puts the chance of exploitation in the next 30 days at 0.33%, the 26th percentile. Fixed in xen 4.13.2-r5.

References

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