CVE-2021-28687 Vulnerability Analysis & Exploit Details

CVE-2021-28687
Vulnerability Scoring

5.5
/10
Significant Risk

Security assessments indicate that CVE-2021-28687 presents a notable risk, potentially requiring prompt mitigation.

Attack Complexity Details

  • Attack Complexity: Low
    Exploits can be performed without significant complexity or special conditions.
  • Attack Vector: Local
    Vulnerability requires local system access.
  • Privileges Required: Low
    Some privileges are necessary to exploit the vulnerability.
  • Scope: Unchanged
    Exploit remains within the originally vulnerable component.
  • User Interaction: None
    No user interaction is necessary for exploitation.

CVE-2021-28687 Details

Status: Modified

Last updated: 🕕 21 Nov 2024, 06:00 UTC
Originally published on: 🕒 11 Jun 2021, 15:15 UTC

Time between publication and last update: 1258 days

CVSS Release: version 3

CVSS3 Source

nvd@nist.gov

CVSS3 Type

Primary

CVSS3 Vector

CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H

CVE-2021-28687 Vulnerability Summary

CVE-2021-28687: HVM soft-reset crashes toolstack libxl requires all data structures passed across its public interface to be initialized before use and disposed of afterwards by calling a specific set of functions. Many internal data structures also require this initialize / dispose discipline, but not all of them. When the "soft reset" feature was implemented, the libxl__domain_suspend_state structure didn't require any initialization or disposal. At some point later, an initialization function was introduced for the structure; but the "soft reset" path wasn't refactored to call the initialization function. When a guest nwo initiates a "soft reboot", uninitialized data structure leads to an assert() when later code finds the structure in an unexpected state. The effect of this is to crash the process monitoring the guest. How this affects the system depends on the structure of the toolstack. For xl, this will have no security-relevant effect: every VM has its own independent monitoring process, which contains no state. The domain in question will hang in a crashed state, but can be destroyed by `xl destroy` just like any other non-cooperating domain. For daemon-based toolstacks linked against libxl, such as libvirt, this will crash the toolstack, losing the state of any in-progress operations (localized DoS), and preventing further administrator operations unless the daemon is configured to restart automatically (system-wide DoS). If crashes "leak" resources, then repeated crashes could use up resources, also causing a system-wide DoS.

Assessing the Risk of CVE-2021-28687

Access Complexity Graph

The exploitability of CVE-2021-28687 depends on two key factors: attack complexity (the level of effort required to execute an exploit) and privileges required (the access level an attacker needs).

Exploitability Analysis for CVE-2021-28687

CVE-2021-28687 presents an accessible attack vector with minimal effort required. Restricting access controls and implementing security updates are critical to reducing exploitation risks.

Understanding AC and PR

A lower complexity and fewer privilege requirements make exploitation easier. Security teams should evaluate these aspects to determine the urgency of mitigation strategies, such as patch management and access control policies.

Attack Complexity (AC) measures the difficulty in executing an exploit. A high AC means that specific conditions must be met, making an attack more challenging, while a low AC means the vulnerability can be exploited with minimal effort.

Privileges Required (PR) determine the level of system access necessary for an attack. Vulnerabilities requiring no privileges are more accessible to attackers, whereas high privilege requirements limit exploitation to authorized users with elevated access.

CVSS Score Breakdown Chart

Above is the CVSS Sub-score Breakdown for CVE-2021-28687, illustrating how Base, Impact, and Exploitability factors combine to form the overall severity rating. A higher sub-score typically indicates a more severe or easier-to-exploit vulnerability.

CIA Impact Analysis

Below is the Impact Analysis for CVE-2021-28687, showing how Confidentiality, Integrity, and Availability might be affected if the vulnerability is exploited. Higher values usually signal greater potential damage.

  • Confidentiality: None
    CVE-2021-28687 has no significant impact on data confidentiality.
  • Integrity: None
    CVE-2021-28687 poses no threat to data integrity.
  • Availability: High
    CVE-2021-28687 can disrupt system operations, potentially causing complete denial of service (DoS).

Exploit Prediction Scoring System (EPSS)

The EPSS score estimates the probability that this vulnerability will be exploited in the near future.

EPSS Score: 0.044% (probability of exploit)

EPSS Percentile: 15.45% (lower percentile = lower relative risk)
This vulnerability is less risky than approximately 84.55% of others.

CVE-2021-28687 References

External References

CWE Common Weakness Enumeration

CWE-909

Vulnerable Configurations

  • cpe:2.3:o:xen:xen:4.12.0:-:*:*:*:*:*:*
    cpe:2.3:o:xen:xen:4.12.0:-:*:*:*:*:*:*
  • cpe:2.3:o:xen:xen:4.12.0:*:*:*:*:*:arm:*
    cpe:2.3:o:xen:xen:4.12.0:*:*:*:*:*:arm:*
  • cpe:2.3:o:xen:xen:4.12.0:*:*:*:*:*:x86:*
    cpe:2.3:o:xen:xen:4.12.0:*:*:*:*:*:x86:*
  • cpe:2.3:o:xen:xen:4.12.0:rc1:*:*:*:*:*:*
    cpe:2.3:o:xen:xen:4.12.0:rc1:*:*:*:*:*:*
  • cpe:2.3:o:xen:xen:4.12.0:rc2:*:*:*:*:*:*
    cpe:2.3:o:xen:xen:4.12.0:rc2:*:*:*:*:*:*
  • cpe:2.3:o:xen:xen:4.12.0:rc3:*:*:*:*:*:*
    cpe:2.3:o:xen:xen:4.12.0:rc3:*:*:*:*:*:*
  • cpe:2.3:o:xen:xen:4.12.0:rc4:*:*:*:*:*:*
    cpe:2.3:o:xen:xen:4.12.0:rc4:*:*:*:*:*:*
  • cpe:2.3:o:xen:xen:4.12.0:rc5:*:*:*:*:*:*
    cpe:2.3:o:xen:xen:4.12.0:rc5:*:*:*:*:*:*
  • cpe:2.3:o:xen:xen:4.12.0:rc6:*:*:*:*:*:*
    cpe:2.3:o:xen:xen:4.12.0:rc6:*:*:*:*:*:*
  • cpe:2.3:o:xen:xen:4.12.0:rc7:*:*:*:*:*:*
    cpe:2.3:o:xen:xen:4.12.0:rc7:*:*:*:*:*:*
  • cpe:2.3:o:xen:xen:4.12.1:*:*:*:*:*:*:*
    cpe:2.3:o:xen:xen:4.12.1:*:*:*:*:*:*:*
  • cpe:2.3:o:xen:xen:4.12.1:*:*:*:*:*:arm:*
    cpe:2.3:o:xen:xen:4.12.1:*:*:*:*:*:arm:*
  • cpe:2.3:o:xen:xen:4.12.1:*:*:*:*:*:x86:*
    cpe:2.3:o:xen:xen:4.12.1:*:*:*:*:*:x86:*
  • cpe:2.3:o:xen:xen:4.12.2:*:*:*:*:*:*:*
    cpe:2.3:o:xen:xen:4.12.2:*:*:*:*:*:*:*
  • cpe:2.3:o:xen:xen:4.12.3:*:*:*:*:*:*:*
    cpe:2.3:o:xen:xen:4.12.3:*:*:*:*:*:*:*
  • cpe:2.3:o:xen:xen:4.12.4:*:*:*:*:*:*:*
    cpe:2.3:o:xen:xen:4.12.4:*:*:*:*:*:*:*
  • cpe:2.3:o:xen:xen:4.13.0:-:*:*:*:*:*:*
    cpe:2.3:o:xen:xen:4.13.0:-:*:*:*:*:*:*
  • cpe:2.3:o:xen:xen:4.13.0:*:*:*:*:*:arm:*
    cpe:2.3:o:xen:xen:4.13.0:*:*:*:*:*:arm:*
  • cpe:2.3:o:xen:xen:4.13.0:*:*:*:*:*:x86:*
    cpe:2.3:o:xen:xen:4.13.0:*:*:*:*:*:x86:*
  • cpe:2.3:o:xen:xen:4.13.0:rc1:*:*:*:*:*:*
    cpe:2.3:o:xen:xen:4.13.0:rc1:*:*:*:*:*:*
  • cpe:2.3:o:xen:xen:4.13.0:rc2:*:*:*:*:*:*
    cpe:2.3:o:xen:xen:4.13.0:rc2:*:*:*:*:*:*
  • cpe:2.3:o:xen:xen:4.13.1:*:*:*:*:*:x86:*
    cpe:2.3:o:xen:xen:4.13.1:*:*:*:*:*:x86:*
  • cpe:2.3:o:xen:xen:4.13.1:*:*:*:*:*:*:*
    cpe:2.3:o:xen:xen:4.13.1:*:*:*:*:*:*:*
  • cpe:2.3:o:xen:xen:4.13.1:*:*:*:*:*:arm:*
    cpe:2.3:o:xen:xen:4.13.1:*:*:*:*:*:arm:*
  • cpe:2.3:o:xen:xen:4.13.2:*:*:*:*:*:x86:*
    cpe:2.3:o:xen:xen:4.13.2:*:*:*:*:*:x86:*
  • cpe:2.3:o:xen:xen:4.13.2:*:*:*:*:*:arm:*
    cpe:2.3:o:xen:xen:4.13.2:*:*:*:*:*:arm:*
  • cpe:2.3:o:xen:xen:4.13.3:*:*:*:*:*:x86:*
    cpe:2.3:o:xen:xen:4.13.3:*:*:*:*:*:x86:*
  • cpe:2.3:o:xen:xen:4.13.3:*:*:*:*:*:arm:*
    cpe:2.3:o:xen:xen:4.13.3:*:*:*:*:*:arm:*
  • cpe:2.3:o:xen:xen:4.13.4:*:*:*:*:*:*:*
    cpe:2.3:o:xen:xen:4.13.4:*:*:*:*:*:*:*
  • cpe:2.3:o:xen:xen:4.14.0:*:*:*:*:*:*:*
    cpe:2.3:o:xen:xen:4.14.0:*:*:*:*:*:*:*
  • cpe:2.3:o:xen:xen:4.14.0:*:*:*:*:*:x86:*
    cpe:2.3:o:xen:xen:4.14.0:*:*:*:*:*:x86:*
  • cpe:2.3:o:xen:xen:4.14.0:*:*:*:*:*:arm:*
    cpe:2.3:o:xen:xen:4.14.0:*:*:*:*:*:arm:*
  • cpe:2.3:o:xen:xen:4.14.1:*:*:*:*:*:*:*
    cpe:2.3:o:xen:xen:4.14.1:*:*:*:*:*:*:*
  • cpe:2.3:o:xen:xen:4.14.1:*:*:*:*:*:arm:*
    cpe:2.3:o:xen:xen:4.14.1:*:*:*:*:*:arm:*
  • cpe:2.3:o:xen:xen:4.14.3:*:*:*:*:*:*:*
    cpe:2.3:o:xen:xen:4.14.3:*:*:*:*:*:*:*
  • cpe:2.3:o:xen:xen:4.15.0:*:*:*:*:*:*:*
    cpe:2.3:o:xen:xen:4.15.0:*:*:*:*:*:*:*
  • cpe:2.3:o:xen:xen:4.15.0:*:*:*:*:*:x86:*
    cpe:2.3:o:xen:xen:4.15.0:*:*:*:*:*:x86:*
  • cpe:2.3:o:xen:xen:4.15.0:rc1:*:*:*:*:*:*
    cpe:2.3:o:xen:xen:4.15.0:rc1:*:*:*:*:*:*

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