Buffer overflow in F5 nginx Gateway Fabric
CVE-2026-42533
A vulnerability exists in NGINX Plus and NGINX Open Source when a map directive uses regex matching and a string expression references the map's regex capture variables before referencing the map output variable. Alternatively, the same result could be achieved by using a non-cacheable variable in a string expression under certain conditions. An unauthenticated attacker along with conditions beyond their control can exploit this vulnerability by sending crafted HTTP requests. This may cause a heap buffer overflow in the NGINX worker process leading to a restart. Additionally, attackers can execute code on systems with Address Space Layout Randomization (ASLR) disabled or when the attacker can bypass ASLR. Impact: This vulnerability may allow remote attackers to cause a denial-of-service (DoS) on the NGINX system or to possibly trigger a code execution. There is no control plane exposure; this is a data plane issue only. Note: Software versions which have reached End of Technical Support (EoTS) are not evaluated.
Vulnerability class: Buffer Overflow
Published · last modified .
CVSS v3 metric
CVSS v3 base score 8.1 (High). Vector: CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:H/A:H.
EPSS exploit prediction
EPSS: 0.009 (58.8th percentile), scored .
Very low probability of exploitation in the next 30 days; routine patching cadence is appropriate. 59th percentile — 58.8% of CVEs in the catalogue have a lower EPSS than this one. How to read EPSS.
EPSS over last 30 days · oldest: 0.045 · newest: 0.009 · change: -0.036
Affected products
- F5 nginx Gateway Fabric
- F5 nginx Ingress Controller — versions 4.0.0, 4.0.1
- F5 nginx Open Source — versions 1.31.2, 0.9.6
- F5 nginx Plus — versions 37.0.0.1, R36, R33
- F5 nginx Plus — versions r36
- F5 Waf
Weakness classification (CWE)
Public proof-of-concept exploits
References
- my.f5.com/manage/s/article/K000162097 (vendor-advisory, patch, Vendor Advisory)
Frequently asked questions
- What is CVE-2026-42533?
- CVE-2026-42533 is a high-severity vulnerability in F5 nginx Gateway Fabric, classified under Heap-based Buffer Overflow. CVSS score: 8.1/10. Published 2026-07-15.
- How severe is CVE-2026-42533?
- High severity. CVSS v3 base score is 8.1 out of 10.
- Is CVE-2026-42533 known to be exploited?
- 14 public proof-of-concept repositories are indexed. Not currently listed in the CISA KEV catalog.