Security readout for executives and security teams
Plain-English summary
A guest virtual machine can make a Linux Xen network backend consume excessive host kernel memory. The business impact is denial of service: a vulnerable virtualization host may become unstable or unavailable if an authorized guest triggers the condition.
Executive priority
Treat this as a virtualization availability risk. It is not described as remotely exploitable from the internet, but it matters where guests are customer-controlled or less trusted. Patch during the next urgent virtualization maintenance window.
Technical view
CVE-2021-28715 affects the Linux netback driver used with Xen networking. Incoming packets are buffered until the guest consumes them. Existing limits can be bypassed because the default stall timeout is long, allowing large memory buildup under fast UDP traffic.
Likely exposure
Exposure is most likely on Xen virtualization hosts using Linux as the network backend for guests, especially where guests are untrusted, tenant-controlled, or network-heavy. Ordinary Linux systems not acting as Xen netback hosts are not indicated by the supplied sources.
Exploitation context
The source bundle does not show CISA KEV listing or active exploitation. The described attack requires guest access and targets availability by exhausting host kernel memory, not confidentiality or integrity.
Researcher notes
This CVE is part of Xen advisory XSA-392 and is distinct from CVE-2021-28714. The supplied text ties CVE-2021-28715 to memory buildup during the 60-second default receive stall timeout.
Mitigation direction
- Review Xen XSA-392 and your Linux distribution advisory for affected kernel versions.
- Apply vendor kernel security updates, including relevant Debian DSA or DLA packages where applicable.
- Prioritize multi-tenant Xen hosts and hosts running untrusted guest workloads.
- If patches are unavailable, follow vendor guidance for temporary mitigations.
- Plan reboots or live-migration workflows needed to activate updated kernels.
Validation and detection
- Inventory Xen hosts using Linux netback for guest networking.
- Compare running kernel versions against Xen XSA-392 and distribution advisories.
- Verify Debian systems include fixes from DSA-5050, DSA-5096, or relevant DLA updates.
- Check host monitoring for unusual kernel memory pressure during guest network activity.
- Confirm vulnerable or unsupported kernels are removed from production pools.
Public sources used
Generated from the cited source records. This long-tail analysis has not been individually reviewed by a named human.
Conservative CVE-to-ATT&CK context
These mappings and lookup hints may be relevant to the vulnerability behavior, CWE, affected product, or exposure path. Glexia-inferred context is not an official MITRE, ATT&CK, CWE, or CVE Program mapping.
ATT&CK lookup starting points
Use these exact CWE pages and searches to review the Glexia ATT&CK library from this CVE's weakness and description context.
CWE-770: Exact CWE lookup
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Open ATT&CK lookupCVE-2021-28715 mapping review
Open the CVE-to-ATT&CK bridge for reviewed, inferred, or future official mappings tied to this CVE.
Open ATT&CK lookup- Severity
- Medium
- CVSS
- 6.5 (3.1)
- Known Exploited
- No
- Published
Vector: CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:C/C:N/I:N/A:H
CNA and ADP enrichment extracted from CVE v5
These fields come from the CVE record and ADP containers, not from Glexia's Take. They preserve time-varying source decisions such as CISA SSVC, KEV status, CVSS metrics, and provider references.
CVSS vector scores
1 official scoreWe collect every scored CVSS vector available in the official CNA and ADP containers. When more than one version is present, the table keeps the source vectors side by side instead of collapsing them into the highest score.
CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:C/C:N/I:N/A:H24Primary CVE scoreVulnerability scoring details
Base CVSS 3.1 score
6.5MediumVector: CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:C/C:N/I:N/A:H
Source materials
- CVE List V5 sourceCVE List V5
- https://xenbits.xenproject.org/xsa/advisory-392.txtCVE reference · x_refsource_MISC
- DSA-5050CVE reference · vendor-advisory, x_refsource_DEBIAN
- [debian-lts-announce] 20220309 [SECURITY] [DLA 2940-1] linux security updateCVE reference · mailing-list, x_refsource_MLIST
- [debian-lts-announce] 20220309 [SECURITY] [DLA 2941-1] linux-4.19 security updateCVE reference · mailing-list, x_refsource_MLIST
- DSA-5096CVE reference · vendor-advisory, x_refsource_DEBIAN
Products and packages named in the record
CWE details
CWE links open Glexia weakness intelligence pages with official CWE context, developer remediation guidance, and related CVE mappings.
Allocation of Resources Without Limits or Throttling
Allocation of Resources Without Limits or Throttling represents a recurring weakness pattern that can create exploitable paths when design, validation, or implementation controls are missing.