Vulnerability in Xen
CVE-2020-25596
An issue was discovered in Xen through 4.14.x. x86 PV guest kernels can experience denial of service via SYSENTER. The SYSENTER instruction leaves various state sanitization activities to software. One of Xen's sanitization paths injects a #GP fault, and incorrectly delivers it twice to the guest. This causes the guest kernel to observe a kernel-privilege #GP fault (typically fatal) rather than a user-privilege #GP fault (usually converted into SIGSEGV/etc.). Malicious or buggy userspace can crash the guest kernel, resulting in a VM Denial of Service. All versions of Xen from 3.2 onwards are vulnerable. Only x86 systems are vulnerable. ARM platforms are not vulnerable. Only x86 systems that support the SYSENTER instruction in 64bit mode are vulnerable. This is believed to be Intel, Centaur, and Shanghai CPUs. AMD and Hygon CPUs are not believed to be vulnerable. Only x86 PV guests can exploit the vulnerability. x86 PVH / HVM guests cannot exploit the vulnerability.
EPSS: 0.005 (40.6th percentile) — read the EPSS interpretation.
CVSS v3 metric
CVSS v3 base score 5.5 (Medium). Vector: CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H.
Affected products
- Xen
- Debian Debian_linux — versions 10.0
- Fedoraproject Fedora — versions 31, 32, 33
- Opensuse Leap — versions 15.2
- N/a — versions n/a
Weakness classification (CWE)
Public proof-of-concept exploits
References
- cve@mitre.org (Patch, x_refsource_MISC, Vendor Advisory)
- cve@mitre.org (x_refsource_FEDORA, vendor-advisory)
- cve@mitre.org (x_refsource_FEDORA, vendor-advisory)
- cve@mitre.org (vendor-advisory, Third Party Advisory, x_refsource_DEBIAN)
- cve@mitre.org (vendor-advisory, Third Party Advisory, x_refsource_SUSE)
- cve@mitre.org (x_refsource_FEDORA, vendor-advisory)
- cve@mitre.org (vendor-advisory, Third Party Advisory, x_refsource_GENTOO)
Frequently asked questions
- What is CVE-2020-25596?
- CVE-2020-25596 is a medium-severity vulnerability in Xen, classified under Improper Neutralization of Special Elements in Output Used by a Downstream Component (Injection). CVSS score: 5.5/10. Published 2020-09-23.
- How severe is CVE-2020-25596?
- Medium severity. CVSS v3 base score is 5.5 out of 10.
- Is CVE-2020-25596 known to be exploited?
- 2 public proof-of-concept repositories are indexed. Not currently listed in the CISA KEV catalog.