CVE-2021-26933
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.
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
What each source reports
NVD Score used 5.5
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 Medium
CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:N/A:N - CVSS 2.0
- 2.1 Low
AV: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-mp78 5.5
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 Medium
CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:N/A:N - Updated
- 2026-11-02
OSVALPINE-CVE-2021-26933 5.5
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 Medium
CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:N/A:N - Updated
- 2026-11-02
OSV 5.5
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 Medium
CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:N/A:N - Updated
- 2026-11-02
OSVDEBIAN-CVE-2021-26933 5.5
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 Medium
CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:N/A:N - Updated
- 2026-11-02
OSVUBUNTU-CVE-2021-26933 5.5
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 Medium
CVSS: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
| Package | Affected | Fixed |
|---|---|---|
xenAlpine:v3.11 | 4.9.0 up to 4.13.2-r5 | 4.13.2-r5 |
xenAlpine:v3.12 | 4.9.0 up to 4.13.2-r5 | 4.13.2-r5 |
xenAlpine:v3.13 | 4.9.0 up to 4.14.1-r2 | 4.14.1-r2 |
xenAlpine:v3.14 | 4.9.0 up to 4.14.1-r3 | 4.14.1-r3 |
xenAlpine:v3.15 | 4.9.0 up to 4.14.1-r3 | 4.14.1-r3 |
xenAlpine:v3.16 | 4.9.0 up to 4.14.1-r3 | 4.14.1-r3 |
xenAlpine:v3.17 | 4.9.0 up to 4.14.1-r3 | 4.14.1-r3 |
xenAlpine:v3.18 | 4.9.0 up to 4.14.1-r3 | 4.14.1-r3 |
xenAlpine:v3.19 | 4.9.0 up to 4.14.1-r3 | 4.14.1-r3 |
xenAlpine:v3.20 | 4.9.0 up to 4.14.1-r3 | 4.14.1-r3 |
Show 16 moreShow less
| Package | Affected | Fixed |
|---|---|---|
xenAlpine:v3.21 | 4.9.0 up to 4.14.1-r3 | 4.14.1-r3 |
xenAlpine:v3.22 | 4.9.0 up to 4.14.1-r3 | 4.14.1-r3 |
xenAlpine:v3.23 | 4.9.0 up to 4.14.1-r3 | 4.14.1-r3 |
xenAlpine:v3.24 | 4.9.0 up to 4.14.1-r3 | 4.14.1-r3 |
xenDebian:12 | before 4.14.1+11-gb0b734a8b3-1 | 4.14.1+11-gb0b734a8b3-1 |
xenDebian:13 | before 4.14.1+11-gb0b734a8b3-1 | 4.14.1+11-gb0b734a8b3-1 |
xenDebian:14 | before 4.14.1+11-gb0b734a8b3-1 | 4.14.1+11-gb0b734a8b3-1 |
xenDebian: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 less4.11.4+37-g3263f257ca-14.11.4+57-g41a822c392-14.11.4+57-g41a822c392-24.11.4-1 | 4.11.4+99-g8bce4698f6-1 |
xenUbuntu: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 less4.6.0-1ubuntu4.14.6.0-1ubuntu4.24.6.0-1ubuntu4.34.6.5-0ubuntu14.6.5-0ubuntu1.14.6.5-0ubuntu1.24.6.5-0ubuntu1.4 | None known |
xenUbuntu:18.04:LTS | All versions, plus listed versions 4.9.0-0ubuntu34.9.0-0ubuntu44.9.2-0ubuntu1 | None known |
xenUbuntu: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 |
xenUbuntu: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 |
xenUbuntu: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 |
xenUbuntu:25.10 | All versions, plus listed versions 4.20.0-1ubuntu14.20.0+68-g35cb38b222-1 | None known |
xenUbuntu: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 |
xenUbuntu: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
| Recorded | Changed | Sources |
|---|---|---|
| affected, facts | ||
| aliases | EUVD | |
| first indexed | CVE 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
xenbits.xen.org/xsa/advisory-364.html
lists.fedoraproject.org/archives/list/package-announce%40lists.fedoraproject.org/message/4GELN5E6MDR5KQBJF5M5COUUED3YFZTD
lists.fedoraproject.org/archives/list/package-announce%40lists.fedoraproject.org/message/EOAJBVAVR6RSCUCHNXPVSNRPSFM7INMP
debian.org/security/2021/dsa-4888
nvd.nist.gov/vuln/detail/CVE-2021-26933
lists.fedoraproject.org/archives/list/package-announce@lists.fedoraproject.org/message/4GELN5E6MDR5KQBJF5M5COUUED3YFZTD
Show 7 moreShow less
lists.fedoraproject.org/archives/list/package-announce@lists.fedoraproject.org/message/EOAJBVAVR6RSCUCHNXPVSNRPSFM7INMP
github.com/advisories/GHSA-3c29-qfhr-mp78
security.alpinelinux.org/vuln/CVE-2021-26933
security-tracker.debian.org/tracker/CVE-2021-26933
ubuntu.com/security/CVE-2021-26933
openwall.com/lists/oss-security/2021/02/16/5
cve.org/CVERecord?id=CVE-2021-26933