CVE-2020-12826
Description
A flaw was found in the Linux kernel loose validation of 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.
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 | 5.3 | 5.3 | N/A |
| Attack Vector | Local | Local | N/A |
| Attack Complexity | Low | Low | 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:L/PR:L/UI:N/S:U/C:L/I:L/A:L
NVD: CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:L/I:L/A:L
Red Hat CVSS v3 Score Explanation
At this time the CIA being high against the kernel component means that the attacker can read / write / crash the system. Which is difficult to do with the given information.
For any of these metrics to be above there must be (from the cvss v3.1 spec doc):
- "There is a total loss of confidentiality,"
- "There is a total loss of integrity or a complete loss of protection"
- "There is a total loss of availability"
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.
Thanks in advance.
Wade Mealing
Understanding the Weakness (CWE)
Access Control
Technical Impact: Bypass Protection Mechanism
In some cases, injectable code controls authentication; this may lead to a remote vulnerability.
Access Control
Technical Impact: Gain Privileges or Assume Identity
Injected code can access resources that the attacker is directly prevented from accessing.
Integrity,Confidentiality,Availability
Technical Impact: Execute Unauthorized Code or Commands
When a product allows a user's input to contain code syntax, it might be possible for an attacker to craft the code in such a way that it will alter the intended control flow of the product. As a result, code injection can often result in the execution of arbitrary code. Code injection attacks can also lead to loss of data integrity in nearly all cases, since the control-plane data injected is always incidental to data recall or writing.
Non-Repudiation
Technical Impact: Hide Activities
Often the actions performed by injected control code are unlogged.
Acknowledgements
Red Hat would like to thank Adam Zabrocki for reporting this issue.
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