CVE-2023-4039: GCC's-fstack-protector fails to guard dynamically-sized local variables on AArch64
**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.
Security readout for executives and security teams
Plain-English summary
CVE-2023-4039 concerns a disputed weakness in stack-protection hardening for AArch64 builds. In certain programs using dynamically sized local variables, GCC-style stack protection may not detect an existing buffer overflow. By itself, this does not create a bug, but it can reduce protection if vulnerable code already exists.
Executive priority
Treat as a defense-in-depth gap, not an emergency standalone compromise. Prioritize teams shipping AArch64 native software, embedded firmware, appliances, or cloud workloads where C/C++ memory safety issues would be business-critical.
Technical view
The issue affects AArch64-targeting GCC-based toolchains when -fstack-protector is used with C99 variable-length arrays or alloca() locals. Statically sized locals are described as protected as intended. The GCC project disputes treating this as a standalone vulnerability, calling it a missed hardening issue. CVSS is 4.8, medium.
Likely exposure
Exposure is most relevant to organizations building AArch64 software with Arm GNU Toolchain or GCC-based toolchains using -fstack-protector, where code contains dynamically sized local variables. Risk depends on whether exploitable buffer overflows exist in the compiled application.
Exploitation context
No active exploitation is identified in the provided sources, and the CVE is not in KEV. Exploitation would require an underlying buffer overflow in affected application code. The weakness may prevent stack protector termination, potentially allowing more serious impact than a controlled crash.
Researcher notes
The record is disputed. The key research question is whether application code has an exploitable overflow involving dynamically sized stack objects. Sources do not name a universal patch. Avoid overstating impact without confirming AArch64, stack-protector use, dynamic stack locals, and a real memory-safety bug.
Mitigation direction
Check Arm and toolchain vendor guidance for updates or recommended actions.
Inventory AArch64 builds that use -fstack-protector.
Audit security-sensitive code for variable-length arrays and alloca() usage.
Fix underlying buffer overflows; do not rely solely on stack protector.
Consider reducing dynamic stack allocation where practical.
Validation and detection
Confirm whether affected binaries target AArch64.
Verify whether builds use -fstack-protector.
Review source for C99 variable-length arrays and alloca().
Prioritize review of code handling untrusted input.
Track vendor advisories for clarified affected versions and fixes.
Generated from the cited source records. This long-tail analysis has not been individually reviewed by a named human.
Potential ATT&CK relevance
Conservative CVE-to-ATT&CK context
These mappings and lookup hints may be relevant to the vulnerability behavior, CWE, affected product, or exposure path. Glexia-inferred context is not an official MITRE, ATT&CK, CWE, or CVE Program mapping.
ATT&CK lookup starting points
Use these exact CWE pages and searches to review the Glexia ATT&CK library from this CVE's weakness and description context.
cwe · low confidence lookup
CWE-693: Exact CWE lookup
Use the exact CWE identifier as the starting point before reviewing related ATT&CK behavior. Open the exact CWE lookup page first, then review the ATT&CK searches from that MITRE weakness context. This is a Glexia lookup hint, not an official ATT&CK mapping.
These fields come from the CVE record and ADP containers, not from Glexia's Take. They preserve time-varying source decisions such as CISA SSVC, KEV status, CVSS metrics, and provider references.
We collect every scored CVSS vector available in the official CNA and ADP containers. When more than one version is present, the table keeps the source vectors side by side instead of collapsing them into the highest score.
CWE links open Glexia weakness intelligence pages with official CWE context, developer remediation guidance, and related CVE mappings.
CWE-693 · source CWE mapping
Protection Mechanism Failure
Protection Mechanism Failure represents a recurring weakness pattern that can create exploitable paths when design, validation, or implementation controls are missing.