Vulnerability Name:

CVE-2020-29487 (CCN-193134)

Assigned:2020-12-15
Published:2020-12-15
Updated:2021-12-10
Summary:An issue was discovered in Xen XAPI before 2020-12-15. Certain xenstore keys provide feedback from the guest, and are therefore watched by toolstack. Specifically, keys are watched by xenopsd, and data are forwarded via RPC through message-switch to xapi. The watching logic in xenopsd sends one RPC update containing all data, any time any single xenstore key is updated, and therefore has O(N^2) time complexity. Furthermore, message-switch retains recent (currently 128) RPC messages for diagnostic purposes, yielding O(M*N) space complexity. The quantity of memory a single guest can monopolise is bounded by xenstored quota, but the quota is fairly large. It is believed to be in excess of 1G per malicious guest. In practice, this manifests as a host denial of service, either through message-switch thrashing against swap, or OOMing entirely, depending on dom0's configuration. (There are no quotas in xenopsd to limit the quantity of keys that result in RPC traffic.) A buggy or malicious guest can cause unreasonable memory usage in dom0, resulting in a host denial of service. All versions of XAPI are vulnerable. Systems that are not using the XAPI toolstack are not vulnerable.
CVSS v3 Severity:7.5 High (CVSS v3.1 Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H)
6.5 Medium (Temporal CVSS v3.1 Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H/E:U/RL:O/RC:C)
Exploitability Metrics:Attack Vector (AV): Network
Attack Complexity (AC): Low
Privileges Required (PR): None
User Interaction (UI): None
Scope:Scope (S): Unchanged
Impact Metrics:Confidentiality (C): None
Integrity (I): None
Availibility (A): High
7.1 High (CCN CVSS v3.1 Vector: CVSS:3.1/AV:L/AC:L/PR:N/UI:N/S:C/C:N/I:N/A:H)
6.2 Medium (CCN Temporal CVSS v3.1 Vector: CVSS:3.1/AV:L/AC:L/PR:N/UI:N/S:C/C:N/I:N/A:H/E:U/RL:O/RC:C)
Exploitability Metrics:Attack Vector (AV): Local
Attack Complexity (AC): Low
Privileges Required (PR): None
User Interaction (UI): None
Scope:Scope (S): Changed
Impact Metrics:Confidentiality (C): None
Integrity (I): None
Availibility (A): High
CVSS v2 Severity:7.8 High (CVSS v2 Vector: AV:N/AC:L/Au:N/C:N/I:N/A:C)
Exploitability Metrics:Access Vector (AV): Network
Access Complexity (AC): Low
Authentication (Au): None
Impact Metrics:Confidentiality (C): None
Integrity (I): None
Availibility (A): Complete
4.9 Medium (CCN CVSS v2 Vector: AV:L/AC:L/Au:N/C:N/I:N/A:C)
Exploitability Metrics:Access Vector (AV): Local
Access Complexity (AC): Low
Athentication (Au): None
Impact Metrics:Confidentiality (C): None
Integrity (I): None
Availibility (A): Complete
Vulnerability Type:CWE-770
Vulnerability Consequences:Denial of Service
References:Source: MITRE
Type: CNA
CVE-2020-29487

Source: XF
Type: UNKNOWN
xen-cve202029487-dos(193134)

Source: GENTOO
Type: Third Party Advisory
GLSA-202107-30

Source: CCN
Type: Xen Security Advisory XSA-354
XAPI: guest-triggered excessive memory usage

Source: MISC
Type: Patch, Vendor Advisory
https://xenbits.xenproject.org/xsa/advisory-354.html

Vulnerable Configuration:Configuration 1:
  • cpe:/o:xen:xapi:*:*:*:*:*:*:*:* (Version < 2020-12-15)

    • Configuration CCN 1:
  • cpe:/a:xensource:xen:*:*:*:*:*:*:*:*

    • * Denotes that component is vulnerable
    BACK
    xen xapi *
    xensource xen *