CVE-2026-42533
HighCVSS 8.1Exploitation Probability (EPSS)
High risk88th percentile - higher than 88% of all known CVEs
Summary
A vulnerability in NGINX Plus and NGINX Open Source occurs when a map directive uses regex matching and a string expression references the map's regex capture variables before referencing the map output variable. An unauthenticated attacker can send crafted HTTP requests, causing a heap buffer overflow in the NGINX worker process, leading to a restart or potential code execution.
Risk Assessment
The risk includes remote denial-of-service (DoS) and potential code execution on systems with ASLR disabled or when ASLR can be bypassed. This is a data plane issue only, with no control plane exposure.
Recommendation
Immediately update NGINX to the latest patched version. If not possible, restrict server access to trusted networks and monitor for unusual HTTP requests.
Other vulnerabilities in NGINX
See all- CVE-2016-1247High
The nginx package before 1.6.2-5+deb8u3 on Debian jessie and earlier versions on Ubuntu and Gentoo allow local users with access to the web server user account to gain root privileges via a symlink attack on the error log.
- CVE-2016-4450High
In nginx before 1.10.1 and 1.11.x before 1.11.1, a vulnerability allows remote attackers to cause a denial of service (NULL pointer dereference and worker process crash) via a crafted request, involving writing a client request body to a temporary file.
- CVE-2016-0742High
The resolver in nginx before 1.8.1 and 1.9.x before 1.9.10 allows remote attackers to cause a denial of service via an invalid pointer dereference, leading to a worker process crash.
- CVE-2014-0133High
Heap-based buffer overflow in the SPDY implementation in nginx 1.3.15 before 1.4.7 and 1.5.x before 1.5.12 allows remote attackers to execute arbitrary code via a crafted request.
- CVE-2026-9256High
A vulnerability in the ngx_http_rewrite_module of NGINX Plus and NGINX Open Source occurs when a rewrite directive uses a regex pattern with overlapping PCRE captures and a replacement string referencing multiple captures. An unauthenticated attacker can send crafted HTTP requests, causing a heap buffer overflow in the NGINX worker process, leading to a restart.
- CVE-2026-42945High
A vulnerability exists in NGINX Plus and NGINX Open Source within the ngx_http_rewrite_module. It occurs when the rewrite directive is followed by rewrite, if, or set directives and an unnamed PCRE capture (e.g., $1, $2) with a replacement string containing a question mark (?). An unauthenticated attacker can send crafted HTTP requests, causing a heap buffer overflow in the NGINX worker process, leading to a restart.
- CVE-2026-27654High
A vulnerability in the NGINX ngx_http_dav_module allows an attacker to trigger a buffer overflow in the NGINX worker process. The issue occurs when the configuration uses MOVE or COPY methods with alias directives and prefix locations.
- CVE-2016-0746Critical
A use-after-free vulnerability in the resolver in nginx versions 0.6.18 through 1.8.0 and 1.9.x before 1.9.10 allows remote attackers to cause a denial of service (worker process crash) or possibly have unspecified other impact via a crafted DNS response related to CNAME response processing.
- CVE-2026-60005High
A vulnerability exists in NGINX Plus and NGINX Open Source within the ngx_http_slice_module module. When the slice directive with unnamed regex captures is configured or during a background cache update, unauthenticated attackers can send requests causing uninitialized memory access in the NGINX worker process, leading to limited memory disclosure or a restart.
- CVE-2026-56434Medium
A vulnerability exists in NGINX Plus and NGINX Open Source within the ngx_http_ssi_module module. This issue occurs when Server-Side Includes (SSI), proxy_pass, and proxy_buffering off directives are configured. An unauthenticated attacker with man-in-the-middle (MITM) capability to control upstream server responses may trigger a use-after-free in the NGINX worker process.
Original NVD description (English source)
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.