# CVE-2026-42945: NGINX ngx_http_rewrite_module vulnerability

- Exploited (CISA KEV): no
- Published: 2026-05-13
- CVSS: 9.2 CRITICAL (v4.0)
- EPSS: 68.0% (99th percentile)
- CWE: CWE-122

NGINX Plus and NGINX Open Source have a vulnerability in the ngx_http_rewrite_module module. This vulnerability exists when the rewrite directive is followed by a rewrite, if, or set directive and an unnamed Perl-Compatible Regular Expression (PCRE) capture (for example, $1, $2) with a replacement string that includes a question mark (?). An unauthenticated attacker along with conditions beyond its 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.  Note: Software versions which have reached End of Technical Support (EoTS) are not evaluated.

## Edge WAF coverage (claimed by vendors, not measured)

| Vendor | Status | First rule | Days after publication |
|---|---|---|---|
| Cloudflare | Blocks by default | 2026-05-15 | 2 |
| AWS | No public claim | — | — |
| Microsoft Azure | No public claim | — | — |
| Google Cloud | No public claim | — | — |
| Fastly | Before feed history | — | — |
| F5 | Rule published | 2026-07-07 | 55 |
| Akamai | No public source | — | — |
| OWASP CRS | No public claim | — | — |

### Cloudflare

- 2026-05-15 · new · rule 2013e3e58efe4b79a26e214f7e52be73 · default Block
  > nginx - Remote Code Execution - Buffer Overread - CVE:CVE-2026-42945. Previous action: N/A. New action: Block. This is a new detection.
  Source: https://developers.cloudflare.com/changelog/post/2026-05-15-emergency-waf-release/
- 2026-05-15 · new · rule 68226e83a4d14ee9a9c878469df0ee6c · default Block
  > nginx - Remote Code Execution - Heap Spray - CVE:CVE-2026-42945. Previous action: N/A. New action: Block. This is a new detection.
  Source: https://developers.cloudflare.com/changelog/post/2026-05-15-emergency-waf-release/

### F5

- 2026-07-07 · new · rule 200011109
  > Added: signature 200011109 "Nginx Rift Buffer Overflow" (Buffer Overflow, risk Low), systems: Nginx. References: CVE-2026-42945.
  Source: https://docs.cloud.f5.com/docs-v2/platform/changelogs/security-details-changelog

## Social

1 posts seen since 2026-11-02.

- Exploit repository (unvetted): https://github.com/basesixtythree/B63-POC-CVE-2026-42945

"No public claim" means no vendor statement names this CVE; "Before feed history" means the CVE is older than the vendor feed. In both cases generic rules may still block it.

HTML: https://cve.vigilbase.com/cve/CVE-2026-42945 · JSON: https://cve.vigilbase.com/api/v1/cves/CVE-2026-42945