Description
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.
Affected products
| Vendor | Product | Affected | Fixed |
|---|---|---|---|
| zlib software | zlib | ≤ 1.3.1.2 | — |
Fixed in Linux distributions
Distributions backport fixes, so the version that fixes this vulnerability differs per release — upgrade to at least the version shown. From the distributions' security trackers and advisories.
Debian
Security tracker ↗| Release | Package | Fixed in | Advisory |
|---|---|---|---|
| Debian 14 | zlib | 1:1.2.6.dfsg-1 | — |
| Debian 13 | zlib | 1:1.2.6.dfsg-1 | — |
| Debian 12 | zlib | 1:1.2.6.dfsg-1 | — |
Ubuntu
Security tracker ↗| Release | Package | Fixed in | Advisory |
|---|---|---|---|
| Ubuntu 26.10 | zsync | No fix yet | — |
| Ubuntu 26.04 LTS | zsync | No fix yet | — |
| Ubuntu 25.10 | zsync | No fix yet | — |
| Ubuntu 22.04 LTS | zsync | No fix yet | — |
| Ubuntu 20.04 LTS | zsync | No fix yet | — |
Alpine
Security tracker ↗| Release | Package | Fixed in | Advisory |
|---|---|---|---|
| Alpine v3.24 | zlib | 1.3.2-r0 | — |
| Alpine v3.23 | zlib | 1.3.2-r0 | — |
| Alpine v3.22 | zlib | 1.3.2-r0 | — |
| Alpine v3.21 | zlib | 1.3.2-r0 | — |
| Alpine v3.20 | zlib | 1.3.2-r0 | — |
Azure Linux
| Release | Package | Fixed in | Advisory |
|---|---|---|---|
| Azure Linux 3 | blosc +2 | No fix yet | — |
| Azure Linux 2 (CBL-Mariner) | blosc +1 | No fix yet | — |
Advisories 6
- WID-SEC-2026-2189 Dell PowerProtect Data Domain: Mehrere Schwachstellen BSI CERT-Bund (WID) · Nov 2, 2026
- ICSA-26-202-06 Siemens CADRA CISA ICS & IT advisories · Jul 21, 2026
- NCSC-2026-0229 Kwetsbaarheden verholpen in Siemens producten NCSC-NL (Netherlands) · Jul 14, 2026
- SSA-470355 SSA-470355: Zlib and Foxit Vulnerabilities in CADRA Siemens ProductCERT · Jul 14, 2026
- WID-SEC-2026-1203 Oracle Fusion Middleware: Mehrere Schwachstellen BSI CERT-Bund (WID) · Apr 21, 2026
- WID-SEC-2026-0045 zlib (untgz utility): Schwachstelle ermöglicht Denial of Service und potenziell Codeausführung BSI CERT-Bund (WID) · Jan 11, 2026
References
- https://seclists.org/fulldisclosure/2026/Jan/3 technical-description exploit
- https://zlib.net/ product
- https://github.com/madler/zlib product
- https://www.vulncheck.com/advisories/zlib-untgz-global-buffer-overflow-in-tgzfname third-party-advisory