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Actively exploited vulnerability

GNU C Library: memory corruption flaw under attack

CVE-2023-4911 · GNU C Library Buffer Overflow Vulnerability

Business software7.8 high

What is affected

GNU C Library is mostly run by companies, schools and public bodies, not on home computers. You are unlikely to have it yourself, but organisations that hold your data may. Breaches that start with flaws like this one are how personal data ends up leaked.

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.

CISA's description

What an attacker can do

This is a memory corruption flaw. It lets an attacker corrupt the program's memory by feeding it specially crafted content: a web page, a file or a network message. The result ranges from a crash to the attacker running their own code.

How it is reached
Needs access to the device or a file opened on it
Access the attacker needs
A basic user account
Does the victim have to do something?
No, works without the victim doing anything

What to do

  1. At home: nothing to install. Keep your own devices updated and use a different password for every service, so that a breach at one organisation does not open your other accounts.
  2. If you administer GNU C Library at work: apply the vendor's fix or mitigation now and review logs for signs of compromise, because the flaw was being exploited before it was listed.
  3. If the product is past its support date and no fix exists, take it off the internet or retire it.

Apply mitigations per vendor instructions or discontinue use of the product if mitigations are unavailable.

Action required by CISA for US federal agencies

Vendor advisories and fixes

How urgent is it

CISA added this vulnerability to its Known Exploited Vulnerabilities catalogue on November 21, 2023, which means there is reliable evidence of attacks in the wild. US federal agencies must fix it by December 12, 2023, a deadline that has already passed. That deadline does not bind anyone else, but it shows how seriously the agency rates it.

The EPSS model estimates a 64% probability that this flaw will be exploited somewhere in the next 30 days. That is higher than 99.2% of all scored vulnerabilities.

Its CVSS severity score is 7.8 out of 10 (high), as recorded in the US National Vulnerability Database.

Technical description

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.

NIST National Vulnerability Database
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