CVE-2020-10711
Description
A NULL pointer dereference flaw was found in the Linux kernel's SELinux subsystem. This flaw occurs while importing the Commercial IP Security Option (CIPSO) protocol's category bitmap into the SELinux extensible bitmap via the' ebitmap_netlbl_import' routine. While processing the CIPSO restricted bitmap tag in the 'cipso_v4_parsetag_rbm' routine, it sets the security attribute to indicate that the category bitmap is present, even if it has not been allocated. This issue leads to a NULL pointer dereference issue while importing the same category bitmap into SELinux. This flaw allows a remote network user to crash the system kernel, resulting in a denial of service.
Statement
This issue affects the versions of the kernel packages as shipped with the Red Hat Enterprise Linux 6 starting with the Red Hat Enterprise Linux 6.7 GA version kernel-2.6.32-573 . Prior Red Hat Enterprise Linux 6 kernel versions are not affected.
Mitigation
Mitigation for this issue is either not available or the currently available options don't meet the Red Hat Product Security criteria comprising ease of use and deployment, applicability to widespread installation base or stability.
This issue can only be resolved by applying updates.
Common Vulnerability Scoring System (CVSS) Score Details
Info alert:Important note
CVSS scores for open source components depend on vendor-specific factors (e.g. version or build chain). Therefore, Red Hat's score and impact rating can be different from NVD and other vendors. Red Hat remains the authoritative CVE Naming Authority (CNA) source for its products and services (see Red Hat classifications).
CVSS v3 Score Breakdown
| Red Hat | NVD | cve.org | |
|---|---|---|---|
| Base Score | 5.9 | 5.9 | N/A |
| Attack Vector | Network | Network | N/A |
| Attack Complexity | High | High | N/A |
| Privileges Required | None | None | N/A |
| User Interaction | None | None | N/A |
| Scope | Unchanged | Unchanged | N/A |
| Confidentiality | None | None | N/A |
| Integrity Impact | None | None | N/A |
| Availability Impact | High | High | N/A |
Vector
Red Hat: CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:N/I:N/A:H
NVD: CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:N/I:N/A:H
Red Hat CVSS v3 Score Explanation
The above score differs in:
AC:H - Because the said NULL pointer dereference occurs against a specific sequence of network packets only, which is difficult to create. Secondly, it requires that network packet labeling by CIPSO v4 format is enabled, It is not enabled by default IIUC. Also, CIPSO v4 packet labeling is likely to be used in a closed network and/or group of systems within a domain of interpretation (DoI).
From: -> https://tools.ietf.org/id/draft-ietf-cipso-ipsecurity-01.txt
- CIPSO Format
Option type: 134 (Class 0, Number 6, Copy on Fragmentation)
This option permits security-related information to be passed between systems within a single Domain of Interpretation (DOI). A DOI is a collection of systems that agree on the meaning of particular values in the security option. An authority that has been assigned a DOI identifier will define a mapping between appropriate CIPSO field values and their human-readable equivalent. This authority will distribute that mapping to hosts within the authority's domain. These mappings may be sensitive, therefore a DOI authority is not required to make these mappings available to anyone other than the systems that are included in the DOI.
Understanding the Weakness (CWE)
Availability
Technical Impact: DoS: Crash, Exit, or Restart
NULL pointer dereferences usually result in the failure of the process unless exception handling (on some platforms) is available and implemented. Even when exception handling is being used, it can still be very difficult to return the software to a safe state of operation.
Integrity,Confidentiality
Technical Impact: Execute Unauthorized Code or Commands; Read Memory; Modify Memory
In rare circumstances, when NULL is equivalent to the 0x0 memory address and privileged code can access it, then writing or reading memory is possible, which may lead to code execution.
Acknowledgements
Red Hat would like to thank Matthew Sheets (gd-ms.com) for reporting this issue.
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