CVE-2021-22555
Description
A flaw was discovered in processing setsockopt IPT_SO_SET_REPLACE (or IP6T_SO_SET_REPLACE) for 32 bit processes on 64 bit systems. This flaw will allow local user to gain privileges or cause a DoS through user name space. This action is usually restricted to root-privileged users but can also be leveraged if the kernel is compiled with CONFIG_USER_NS and CONFIG_NET_NS and the user is granted elevated privileges.
Statement
In Red Hat Enterprise Linux 7, only privileged users can trigger this bug. In Red Hat Enterprise Linux 8 a regular user can trigger it, however the result is corruption of 4 bytes of memory.
Mitigation
The mitigation for the Red Hat Enterprise Linux 8 is to disable unprivileged users from running unshare(CLONE_NEWUSER) or unshare(CLONE_NEWNET) that could be done with this command:
echo 0 > /proc/sys/user/max_user_namespaces
For making this change in configuration permanent.
Note: User namespaces are used primarily for Linux containers. If containers are in use, this requirement is not applicable.
Configure RHEL 8 to disable the use of user namespaces by adding the following line to a file in the "/etc/sysctl.d/" directory:
user.max_user_namespaces = 0
The system configuration files need to be reloaded for the changes to take effect. To reload the contents of the files, run the following command:
$ sudo sysctl --system
The other mitigation for containers, if without disabling user namespaces, is blocking the pertinent syscalls in a seccomp policy file. For more information about seccomp, please read: https://www.openshift.com/blog/seccomp-for-fun-and-profit
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 | 7.8 | 7.8 | 8.3 |
| Attack Vector | Local | Local | Adjacent Network |
| Attack Complexity | Low | Low | High |
| Privileges Required | Low | Low | None |
| User Interaction | None | None | None |
| Scope | Unchanged | Unchanged | Changed |
| Confidentiality | High | High | High |
| Integrity Impact | High | High | High |
| Availability Impact | High | High | High |
Vector
Red Hat: CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H
NVD: CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H
cve.org: CVSS:3.1/AV:A/AC:H/PR:N/UI:N/S:C/C:H/I:H/A:H
Understanding the Weakness (CWE)
Integrity
Technical Impact: Modify Memory; Execute Unauthorized Code or Commands
Write operations could cause memory corruption. In some cases, an adversary can modify control data such as return addresses in order to execute unexpected code.
Availability
Technical Impact: DoS: Crash, Exit, or Restart
Attempting to access out-of-range, invalid, or unauthorized memory could cause the product to crash.
Other
Technical Impact: Unexpected State
Subsequent write operations can produce undefined or unexpected results.
Frequently Asked Questions
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