zlib is a ubiquitous compression library; a heap overflow can crash or enable RCE across many widely used products and libraries.
CVE-2026-85091
Heap overflow in zlib gz_vacate via gzwrite/gzprintf (v1.3.1.2–1.3.2)
Is CVE-2026-85091 being exploited?
Not confirmed. CVE-2026-85091 does not appear in CISA's Known Exploited Vulnerabilities catalog, which records only exploitation that has been observed and reported publicly. That is evidence of absence of a report, not evidence the flaw is unattacked. EPSS currently estimates a 0.44% probability of exploitation in the next 30 days.
How severe is CVE-2026-85091?
CVE-2026-85091 is rated High with a CVSS score of 8.3. Severity describes how bad exploitation would be, not how likely it is: pair it with exploitation evidence before deciding what to patch first.
Is there a patch for CVE-2026-85091?
Not known from our data. No patch reference has been recorded for CVE-2026-85091, which is not the same as no patch existing — a fix may have shipped without a tagged reference, or after this record was written. The vendor advisory is the only authority on whether a fix exists, and mitigations may be available regardless.
What does CVE-2026-85091 affect?
CVE-2026-85091 affects zlib 1.3.1.2 - 1.3.2, Any software using zlib gz* API (gzwrite/gzprintf/gzvprintf). Confirm the exact affected versions against the vendor advisory before deciding you are exposed.
What should I do about CVE-2026-85091?
Audit and patch zlib-dependent apps, avoid non-blocking gzwrite/gzprintf, deploy vendor fix when released
Exploitation status reflects CISA's KEV catalog as we last synced it. Check the catalog directly.
Heap buffer overflow via gzprintf/gzvprintf after non-blocking gzwrite stalls, causing memory corruption, crashes, or potential remote code execution in apps using zlib.
Immediate action required
- affected>= 1.3.1.2 and <= 1.3.2
As published in the CVE Program record. A version outside these ranges is not a statement that it is unaffected — vendors sometimes understate a range, and distribution-backported builds carry upstream numbers that do not reflect what was patched into them.