CVE-2026-22184

zlib versions up to and including 1.3.1.2 include a global buffer overflow in the untgz utility located under contrib/untgz. The vulnerability is limited to the standalone demonstration utility and does not affect the core zlib compression library. The flaw occurs when a user executes the untgz command with an excessively long archive name supplied via the command line, leading to an out-of-bounds write in a fixed-size global buffer.

What this means for your business

It affects Zlib. It matters if your company, or a supplier that handles your data, runs it.
An attacker can use it only with access to the machine itself, with an ordinary user login, and without anyone at your company clicking anything.
FIRST's prediction model gives it a 0.4% chance of attack attempts being seen in the next 30 days, ranking above 35% of all known flaws.

What to do

1Check whether your company or your suppliers run Zlib, and which version. The affected versions are listed further down this page.
2If you do, follow the vendor's guidance. No patch reference has been published yet.

Not sure if your company is exposed?

Fastnexa’s certified penetration testers can check whether attackers could use this flaw, or others like it, against your websites, apps and network. The full test is free for our first 10 founding clients until 31 December 2026.

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Scoring

CVSS: 7.8 (v3.1)
Vector: CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H
CVSS v4: 4.6
Weakness: CWE-787
Assigned by: disclosure@vulncheck.com

Dates

Published: 2026-01-07
Last modified: 2026-09-01
Sources: NVD

Affected products

Zlib Zlib- 1.3.1.2

As listed in the NVD configuration data. Not a statement about your estate.