CVE Intelligence
Medium exploit reference

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.

Published Sep 13, 2023 · Updated Oct 14, 2026 · Sources: NIST National Vulnerability Database, CVE Program (cve.org) e CISA ADP · CNA: Arm

Who exploits it and how urgent it is

A 0–100 score combining confirmed exploitation, ransomware and APT use, public exploits, EPSS and severity.

No exploitation signal in the sources consulted so far.
How the score was calculated
  • EPSS 0.8% (30-day exploitation probability)+8
  • Technical severity (medium)+3
  • CISA SSVC: exploitation "poc"+5

The score orders the patch queue; it does not replace your asset context (internet exposure, criticality, compensating controls).

Triage

Is it exploited, how likely is exploitation, what does it touch, and how severe do the sources call it.

Exploitation
Not confirmed
Not in CISA KEV — an absence of record, not proof it is unexploited.
EPSS FIRST
0.76%
ahead of 54% of scored CVEs · Oct 14, 2026
Affects
Arm
Arm GNU Toolchain and 1 more
CVSS base
4.8
Medium · 3 source(s)

CISA SSVC assessment CISA

Three decision points CISA publishes for the CVEs it assesses (SSVC 2.0.3). A stakeholder decision, not a severity score.

Exploitation
Proof of concept
none · proof-of-concept · active
Automatable
No
can an attacker script the kill-chain steps
Technical impact
Partial
partial · total control of the vulnerable component

Remediation

Fixes and mitigations documented by the sources — linked to the original advisory.

  • Documented patch — developer.arm.com (NIST National Vulnerability Database)
  • Documented patch — github.com (NIST National Vulnerability Database)

First 24 hours

Ordered from the record’s own fields — exposure first, because you cannot patch what you have not found. A rule-generated starting point.

  1. Identify exposed assets running the affected vendor/product/version combinations (Arm Arm GNU Toolchain, Gnu Gcc).
  2. The attack is network-based and needs no privileges: restrict exposure (ACLs, VPN, WAF) until patched.
  3. Apply the fixed version or the patch documented under Remediation.
  4. Search available logs for exploit probes, errors and authentication anomalies.

Affected scope

Vendor, product and versions as the sources word them.

VendorProductVersionsStatusSource
Arm Arm GNU Toolchain version All versions where option -fstack-protector is used Vulnerable CVE Program (cve.org) e CISA ADP
Gnu Gcc < 2023-09-12 Vulnerable NIST National Vulnerability Database
Gnu Gcc version All versions of GCC that target AArch64 when option -fstack-protector is used Vulnerable CVE Program (cve.org) e CISA ADP

Attack characteristics

The CVSS vector, decoded. It describes the attack, not your exposure to it.

Attack vector
Network
Attack complexity
High
Privileges required
None
User interaction
None
Scope
Unchanged
Confidentiality
Low
Integrity
Low
Availability
None

Every base score collected

Sources score independently and may disagree; each row says who scored it and under which version.

ScoreVersionSeverityExpl.ImpactScored by
4.8 CVSS 3.1 Medium 2.2 2.5 arm-security@arm.com via NIST National Vulnerability Database
4.8 CVSS 3.1 Medium 2.2 2.5 nvd@nist.gov via NIST National Vulnerability Database
4.8 CVSS 3.1 Medium — — Arm via CVE Program (cve.org) e CISA ADP
CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:L/I:L/A:N (score shown at the top: nvd@nist.gov)

Weakness MITRE

Weakness class according to MITRE’s CWE catalog.

CWE-693

Other CVEs with this weakness →

Detection

Read off the CVSS vector and the weakness class. Starting points, not tested rules.

  • Prioritize edge telemetry for the network-reachable component (proxy, WAF, IDS/IPS).
web/proxy/WAF logsnetwork IDS/IPS

Timeline

What happened to this CVE, newest first.

  • 2026
  • Affected products added · arm ltd/arm gnu toolchain, gnu/gcc
    Oct 14, 2026 · CVE Program (cve.org) e CISA ADP
  • SSVC assessment updated
    Oct 14, 2026 · CVE Program (cve.org) e CISA ADP
  • Record published
    Oct 14, 2026
  • Fix documented
    Oct 14, 2026 · NIST National Vulnerability Database
  • Affected products added · gnu/gcc
    Oct 14, 2026 · NIST National Vulnerability Database
  • CVSS changed · 4.8
    Oct 14, 2026 · NIST National Vulnerability Database
  • Source status changed · → Modified
    Oct 14, 2026 · NIST National Vulnerability Database
  • Record created in this database
    Oct 14, 2026 · Alertas do Telegram
  • 2023
  • CVE published
    Sep 13, 2023 · Arm

Source activity

Repeated readings are counted rather than listed.

  • 1× References added · Oct 14, 2026 – Oct 14, 2026
  • 1× Official description updated · Oct 14, 2026 – Oct 14, 2026

References

4 on the record

Elsewhere on this site

Arm
every CVE for this vendor
CWE-693
other pages naming this weakness

Related CVEs (same products)

  • CVE-2021-3826 Buffer Errors (Improper Restriction of Operations within Memory Bounds) in Gnu Gcc Sep 1, 2022
  • CVE-2022-27943 libiberty/rust-demangle.c in GNU GCC 11.2 allows stack consumption in demangle_const, as... Mar 26, 2022
  • CVE-2021-46195 GCC v12.0 was discovered to contain an uncontrolled recursion via the component libiberty/rust... Jan 14, 2022
  • CVE-2019-15847 The POWER9 backend in GNU Compiler Collection (GCC) before version 10 could optimize multiple... Sep 2, 2019
  • CVE-2018-12886 stack_protect_prologue in cfgexpand.c and stack_protect_epilogue in function.c in GNU Compiler... May 22, 2019

Not in any source we poll

Listed rather than left blank: an empty field and an unmeasured one look identical on screen, and only one is a reason to look elsewhere.

  • No confirmed IOCs, IP addresses, domains, file hashes, or malware artifacts supplied.
  • No organization-specific asset inventory, compensating-control status, or patch deployment evidence supplied.
  • No exploit packet captures, log samples, or incident case IDs supplied.

Answered from this record

Text assembled only from the fields above — no additional claims.

What should defenders know first?

CVE-2023-4039 is "GCC's-fstack-protector fails to guard dynamically-sized local variables on AArch64", rated Medium. It affects Arm GNU Toolchain (Arm); versions are in the scope table. It is not in CISA KEV, which does not rule out exploitation. CVSS 4.8 describes technical severity. EPSS 0.76% estimates the probability of exploitation in 30 days; neither replaces your asset context. First verify whether exposed or business-critical assets run the affected versions, apply vendor fixes or mitigations, and preserve logs for review.

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