CVE-2020-35508
Description
A flaw possibility of race condition and incorrect initialization of the process id was found in the Linux kernel child/parent process identification handling while filtering signal handlers. A local attacker is able to abuse this flaw to bypass checks to send any signal to a privileged process.
Statement
The incorrect initialization of the process id affects Red Hat Enterprise Linux only.
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.
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 | 4.5 | 4.5 | N/A |
| Attack Vector | Local | Local | N/A |
| Attack Complexity | High | High | N/A |
| Privileges Required | Low | Low | N/A |
| User Interaction | None | None | N/A |
| Scope | Unchanged | Unchanged | N/A |
| Confidentiality | Low | Low | N/A |
| Integrity Impact | Low | Low | N/A |
| Availability Impact | Low | Low | N/A |
Vector
Red Hat: CVSS:3.1/AV:L/AC:H/PR:L/UI:N/S:U/C:L/I:L/A:L
NVD: CVSS:3.1/AV:L/AC:H/PR:L/UI:N/S:U/C:L/I:L/A:L
Red Hat CVSS v3 Score Explanation
The possible scenario of attack is that unprivileged process can send signal to init if init obtained a small enough self_exec_id during booting process. This issue is similar to CVE-2020-12826 ("a local user is able to bypass checks to send any signal to a privileged process"), and the explanation of CVSS difference of CIA:L is: "The attacker in this example is attacking userspace components from a kernel bug. The 'highest value' they could attack is userspace programs running at a privilege level higher than their local system.
This would mean attacking setuid or applications running as root. For these processes, they mostly already handle signals (SIGHUP, SIGKILL) and will respond as if the attacker's request is coming from a legit parent. The process will terminate or reload the configuration or perform an action that they had already programmed for. It can not perform an action that the developer had not intended within the signal handler, these handlers are written with intent to handle a signal.
With this in mind the attacker -still- only has access to the userspace functionality of the issue and not kernel internals or other process memory. They can only create a situation in which the daemons attack vectors are being exploited, they do not have arbitrary control of what to read/write/crash.
This to me immediately drops the flaw from C:H I:H A:H to C:L I:L A:L , considering these attack vectors."
Understanding the Weakness (CWE)
Confidentiality
Technical Impact: Read Memory; Read Application Data
When reusing a resource such as memory or a program variable, the original contents of that resource may not be cleared before it is sent to an untrusted party.
Access Control
Technical Impact: Bypass Protection Mechanism
If security-critical decisions rely on a variable having a "0" or equivalent value, and the programming language performs this initialization on behalf of the programmer, then a bypass of security may occur.
Availability
Technical Impact: DoS: Crash, Exit, or Restart
The uninitialized data may contain values that cause program flow to change in ways that the programmer did not intend. For example, if an uninitialized variable is used as an array index in C, then its previous contents may produce an index that is outside the range of the array, possibly causing a crash or an exit in other environments.
Acknowledgements
Red Hat would like to thank Eddy Wu (trendmicro.com) for reporting this issue.
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