Actively exploited

CVE-2023-4911 GNU C Library Buffer Overflow Vulnerability

GNU C Library's dynamic loader ld.so contains a buffer overflow vulnerability when processing the GLIBC_TUNABLES environment variable, allowing a local attacker to execute code with elevated privileges.

From the CISA KEV catalogue version 2026.11.06, with Cybergen analysis. Updated 6 Nov 2026.

Our Assessment

Should You Worry?

Patch urgentlyCybergen assessment

CISA confirmed exploitation in the wild and added it to the Known Exploited Vulnerabilities catalogue on 21 Nov 2023.
Rated High severity (CVSS 7.8, scored by Vendor).
It has been in the catalogue for 1,081 days. Systems still unpatched now have almost certainly been scanned for it.

The Vulnerability

What It Is

A buffer overflow was discovered in the GNU C Library's dynamic loader ld.so while processing the GLIBC_TUNABLES environment variable. This issue could allow a local attacker to use maliciously crafted GLIBC_TUNABLES environment variables when launching binaries with SUID permission to execute code with elevated privileges.

Affected Versions

Product	Versions
GNU C Library	2.34 to before 2.39
Red Hat Red Hat Enterprise Linux 8	See the vendor advisory
Red Hat Red Hat Enterprise Linux 8	See the vendor advisory
Red Hat Red Hat Enterprise Linux 8.6 Extended Update Support	See the vendor advisory
Red Hat Red Hat Enterprise Linux 9	See the vendor advisory
Red Hat Red Hat Enterprise Linux 9	See the vendor advisory

From the public CVE record, as supplied by the vendor. Always confirm against the vendor advisory.

From Watch to Action

What To Do Now

1
Find it
Search your asset inventory and external attack surface for GNU C Library. Include cloud images, appliances and anything a supplier runs for you.
Attack Surface Management
2
Fix it
Apply mitigations per vendor instructions or discontinue use of the product if mitigations are unavailable.
Vulnerability Management
3
Hunt for compromise
If an affected system was reachable before you patched, assume it may have been hit. Check logs, new accounts, web shells and outbound connections from the date of exposure.
Incident Response
4
Prove it is fixed
Rescan or test the system after patching. Upgrades that fail silently and forgotten secondary instances are common.
Penetration Testing

Vendor Advisories

nvd.nist.gov/vuln/detail/CVE-2023-4911

Regulation

The Compliance Clock

Cyber EssentialsRated high, so if it affects devices in your Cyber Essentials scope, the update must be installed within 14 days of the vendor releasing it.NIS2If exploitation causes a significant incident, essential and important entities owe their CSIRT an early warning within 24 hours and a notification within 72 hours.DORAFinancial entities must classify ICT incidents and send an initial notification for a major incident within strict deadlines, with exploited flaws a common cause.US federal (BOD 22-01)Federal civilian agencies had until 12 Dec 2023 to remediate. A sensible benchmark for everyone else.

General guidance, not legal advice. Your obligations depend on your sector, scope and jurisdiction.

Stay Ahead

More Exploited GNU Flaws

All 5 exploited GNU vulnerabilities

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CVE-2023-4911 GNU C Library Buffer Overflow Vulnerability

Should You Worry?

What It Is

Affected Versions

What To Do Now

Find it

Fix it

Hunt for compromise

Prove it is fixed

Vendor Advisories

The Compliance Clock

More Exploited GNU Flaws

Not Sure If You Are Exposed?

Sources