CVE-2023-4039Public exploitNetwork attack vector

Control-flow hijack via unguarded dynamic stack allocations

Published Sep 13, 2023 · Updated Jun 23, 2026

Protection failure in GNU Compiler Collection and Arm GNU Toolchain allows attackers to bypass AArch64 stack canaries. The AArch64 backend places dynamically allocated locals below saved registers while the canary remains above them, so a contiguous overflow can overwrite frame and link registers without touching the guard. Exploitation requires a separate overflow in a C99 variable-length array, alloca() object, or variable-sized by-value argument; bypassing the guard permits a crash or compromise of confidentiality and integrity.

CVSS severity4.8
Medium
EPSS probability0.76%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
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Summary

What happened

Protection failure in GNU Compiler Collection and Arm GNU Toolchain allows attackers to bypass AArch64 stack canaries. The AArch64 backend places dynamically allocated locals below saved registers while the canary remains above them, so a contiguous overflow can overwrite frame and link registers without touching the guard. Exploitation requires a separate overflow in a C99 variable-length array, alloca() object, or variable-sized by-value argument; bypassing the guard permits a crash or compromise of confidentiality and integrity.

The record

CVE
CVE-2023-4039
Published
Sep 13, 2023
Updated
Jun 23, 2026
Vendor
GNU Project
Product
GNU Compiler Collection
Classifications
CWE-693
Attack vector
network
Privileges
unauthenticated

Timeline

How it unfolded

  1. Sep 13, 2023CVE publishedPublication date reported by the CVE source.
  2. Jun 23, 2026Record updatedLatest update available in the CVE record.

Exploitability

Present is not the same as exploitable

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Is a vulnerable build present?

Compare these published version ranges with your installed build and any vendor patches.

  1. Affected versionversion=All versions of GCC that target AArch64 when option -fstack-protector is used

What conditions does exploitation require?

Attack vectornetwork
Required privilegesunauthenticated

What is affected?

GNU Project · GNU Compiler Collectionversion=All versions of GCC that target AArch64 when option -fstack-protector is used
Arm · Arm GNU Toolchainversion=All versions where option -fstack-protector is used

Published CVSS scores

4.8Arm LimitedCVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:L/I:L/A:N

CVSS describes severity. EPSS estimates exploitation probability.

Attacks

What attackers are doing with it

Daily unique IPs observed by Shadowserver honeypots for known exploited vulnerabilities (KEVs). Missing observations do not establish an absence of attacks.

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No observations available

Sep 10, 2026Sep 16, 2026
Latest reporting daySep 16, 2026
Latest daily unique IPsUnavailable
Prior 30-day averageUnavailable
SourceShadowserver honeypots (KEV)
Vectornetwork
Privilegesunauthenticated
Known exploitationUnconfirmed
Public exploitPublished

Weakness, pattern, technique

CWE-693Protection Mechanism Failure

Public exploit references

Labels summarize the accepted research assessment. They do not indicate a test against your environment.

Technologies

Your stack

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Your stack

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