Affects widely deployed NGINX (Open Source and Plus); remote DoS and possible RCE could disrupt web infrastructure broadly.
CVE-2026-42533
NGINX heap overflow in map regex handling allows remote DoS and possible code execution.
Is CVE-2026-42533 being exploited?
Not confirmed. CVE-2026-42533 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 4.5% probability of exploitation in the next 30 days.
How severe is CVE-2026-42533?
CVE-2026-42533 is rated Critical with a CVSS score of 9.2. 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-2026-42533?
Yes. A fix has been recorded for CVE-2026-42533. The vendor advisory is the authority on the exact fixed version — apply it from there rather than from a summary.
What does CVE-2026-42533 affect?
CVE-2026-42533 affects NGINX Open Source, NGINX Plus, NGINX instances using map with regex capture vars or non-cacheable vars in string expressions. Confirm the exact affected versions against the vendor advisory before deciding you are exposed.
What should I do about CVE-2026-42533?
Apply vendor patch when available; avoid regex captures/non-cacheable vars in map string expressions and limit external exposure.
Exploitation status reflects CISA's KEV catalog as we last synced it. Check the catalog directly.
Remote attacker can send crafted HTTP requests to trigger heap buffer overflow causing worker restart (DoS) and possibly remote code execution if ASLR is bypassed.
Immediate action required
- affected>= 1.31.2 and < 1.31.3
- affected>= 0.9.6 and < 1.30.4
- affected>= 37.0.0.1 and < 37.0.3.1
- affected>= R36 and < R36 P7
- affected>= R33 and < *
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.