CVE-2021-20294
Description
A flaw was found in binutils' readelf program. An attacker who is able to convince a victim using readelf to read a crafted file, could trigger a stack buffer overflow, out-of-bounds write of arbitrary data supplied by the attacker. The highest impact of this flaw is to confidentiality, integrity, and availability.
Statement
The issue is classified as moderate severity primarily because binutils is not typically exposed to untrusted inputs in most environments, limiting its exploitation potential. The buffer overflow only triggers during the parsing of malformed ELF files, which would require an attacker to convince a user to process a malicious ELF file with readelf. Moreover, binutils does not handle privileged operations, meaning exploitation is unlikely to lead to system compromise or escalation of privileges. Additionally, the impact is localized to the application itself, without affecting the broader system or network security.
As per upstream binutils security policy this issue is not considered as a security flaw. Basically the key element of the policy that affects this is the understanding that analysis of untrusted binaries must always be done in a sandbox because the ELF format is open ended enough to make the analysis tools do anything, like including and processing arbitrary files. This eliminates the only possible vulnerability vector here, which is the possibility of a user being tricked into downloading and analyzing an untrusted ELF without sandboxing.
See the binutils security policy for more details: https://sourceware.org/cgit/binutils-gdb/tree/binutils/SECURITY.txt
Mitigation
Stack canaries, non-executable stack (NX), address space layout randomization (ASLR) are binary hardening protections enabled in Red Hat Enterprise Linux 7 and 8 that should greatly limit the impact of this flaw. An additional mitigation is to not use readelf to read files from untrusted sources.
To learn more about binary hardening protections in Red Hat Enterprise Linux, please see https://access.redhat.com/articles/65299
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).
The following CVSS metrics and score provided are preliminary and subject to review.
CVSS v3 Score Breakdown
| Red Hat | NVD | cve.org | |
|---|---|---|---|
| Base Score | 7 | 7.8 | N/A |
| Attack Vector | Local | Local | N/A |
| Attack Complexity | High | Low | N/A |
| Privileges Required | None | None | N/A |
| User Interaction | Required | Required | N/A |
| Scope | Unchanged | Unchanged | N/A |
| Confidentiality | High | High | N/A |
| Integrity Impact | High | High | N/A |
| Availability Impact | High | High | N/A |
Vector
Red Hat: CVSS:3.1/AV:L/AC:H/PR:N/UI:R/S:U/C:H/I:H/A:H
NVD: CVSS:3.1/AV:L/AC:L/PR:N/UI:R/S:U/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.
Acknowledgements
Red Hat would like to thank Hao Wang for reporting this issue.
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