NewsCompaniesFlawsGuides
Get the app

CVE-2023-4911

From Exploited flaws, HARD’s guide to the flaws being used in attacks · Checked
This article is about a flaw in GNU C Library. For every flaw being used in attacks, see Exploited flaws; for GNU’s, see GNU flaws being used in attacks.

CVE-2023-4911 is a security flaw in GNU C Library. Someone who already has a way in can use GNU C Library to run their own code. The US Cybersecurity and Infrastructure Security Agency (CISA) added it to its catalog of flaws known to be used in attacks on 21 Nov 2023.[1]

GNU C Library is business software or equipment. Most families won’t have it, but attackers break into it to get inside companies, and from there to what those companies hold about their customers, patients and staff. Fixed in version 2.39 and V1.1.

Description

CISA calls it a c library buffer overflow in GNU GNU C Library. In its words: “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.”[1]

The CVE record adds: “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.”[2]

The underlying weakness is heap buffer overflow (CWE-122), in MITRE’s list of common software weaknesses.

It scores 7.8 out of 10 on the Common Vulnerability Scoring System, which rates it high, scored by NVD using CVSS 3.1.[2]

Affected versions

NVD’s record lists these fixed versions: in each line, everything before the version shown is affected.[2]

ProductFixed in
GNU C Library2.39
SIMATIC S7-1500 TM MFP - GNU/Linux subsystemV1.1

Most families won’t have GNU C Library; it’s for whoever looks after IT at work.

Exploitation

CISA added it to its catalog of known exploited vulnerabilities on 21 Nov 2023, 49 days after it was made public. CISA lists a flaw only when it has reliable evidence of it being exploited, and gave US federal agencies until 12 Dec 2023 to fix it.[1]

FIRST’s Exploit Prediction Scoring System, which estimates how likely a flaw is to be used in attacks in the next 30 days from what it sees across the internet, puts it at 64%. That’s in the top 1% of the flaws it scores.[4]

CISA assesses it as not automatable: each attack takes some work.

CISA doesn’t say who was attacked, or how.

Fix

GNU has published a fix or advice.[3] CISA’s required action: “Apply mitigations per vendor instructions or discontinue use of the product if mitigations are unavailable.”[1]

  1. Check whether you use it.GNU C Library is business software or equipment, so most families won’t have it. If you run a business, or work from home on company equipment, ask whoever looks after your IT.
  2. Send this page to your IT person.Ask them to confirm it’s fixed (fixed in version 2.39 and V1.1), or not in use. CISA gave US government agencies until 12 Dec 2023 to fix it.
  3. If it can’t be fixed, take it offline.CISA’s advice when there’s no fix is to stop using the product, or take it off the internet, until there is one.

You can’t fix someone else’s server, but you can watch for what follows a break-in like this: a breach notice, a password reset you didn’t ask for, or a scam message that knows things it shouldn’t. HARD watches for those for you and your family.

Timeline

DateEvent
The flaw is made public in the National Vulnerability Database, with a severity score of 7.8.[2]
CISA adds it to its catalog of flaws known to be used in attacks.[1]
CISA’s deadline for US government agencies to fix it.[1]
FIRST puts the odds of it being used in attacks in the next 30 days at 64%.[4]

See also

Other GNU flaws

  • CVE-2026-24061, GNU InetUtils: argument injection ·
  • CVE-2014-6278, GNU Bash: bash OS command injection ·
  • CVE-2014-7169, GNU Bourne-Again Shell (Bash): arbitrary code execution ·
  • CVE-2014-6271, GNU Bourne-Again Shell (Bash): arbitrary code execution ·

Other heap buffer overflow flaws

  • CVE-2026-94127, F5 BIG-IP APM: heap-based buffer overflow ·
  • CVE-2025-25249, Fortinet products: heap-based buffer overflow ·
  • CVE-2026-85880, Microsoft Windows: heap-based buffer overflow ·
  • CVE-2025-32706, Microsoft Windows: common log file system (CLFS) driver heap-based buffer overflow ·
  • CVE-2025-24993, Microsoft Windows: NTFS heap-based buffer overflow ·

Every GNU flaw on CISA’s list · Everything added in November 2023

References

  1. ^ Cybersecurity and Infrastructure Security Agency. “GNU C Library Buffer Overflow Vulnerability”. Known Exploited Vulnerabilities Catalog, added 21 Nov 2023.
  2. ^ National Institute of Standards and Technology. “CVE-2023-4911 Detail”. National Vulnerability Database, published 3 Oct 2023.
  3. ^ GNU. Advisories and fixes: sourceware.org, access.redhat.com, debian.org, bugzilla.redhat.com.
  4. ^ FIRST. “Exploit Prediction Scoring System”. EPSS 0.638, percentile 99.2, 31 Oct 2026.
  5. CVE Program. “CVE-2023-4911”. The official CVE record.

This article is built from CISA’s catalog (version 2026.10.30), NVD’s record and FIRST’s scores, kept in HARD’s database and checked every morning. The plain English is HARD’s.