CVE-2026-42945
HIGH · 8.1Working PoC public, vendors patching urgently, credible signal but marketing hyperbole inflates severity claims.
What: Heap buffer overflow in NGINX's ngx_http_rewrite_module triggered by crafted HTTP requests combining rewrite directives with unnamed PCRE captures and question marks in replacement strings. Affects NGINX Plus and Open Source; CVSS 8.1 (HIGH). RCE possible on systems without ASLR.
Why it matters: Public PoC disclosed on GitHub within 24 hours of CVE publication. Social chatter references working exploit code and urgent patching (versions 1.30.1, 1.31.0). Not yet KEV-listed but high engagement across security communities and active vendor response signaling. 18-year-old dormant flaw now weaponized.
Where it's seen: Security news outlets (The Hacker News, SecurityOnline) headline "RCE" and "critical"; threat intelligence accounts drop PoC links; defenders discussing patch timelines and config detection; marketers amplifying with "hijack one-third of internet" framing.
RISK: HIGH — Public PoC, RCE vector, widespread NGINX deployment, no KEV-listing yet but urgent patching underway.
Description
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, for systems with Address Space Layout Randomization (ASLR ) disabled, code execution is possible. Note: Software versions which have reached End of Technical Support (EoTS) are not evaluated.
CVSS 3.1 breakdown
CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:H/A:H- Attack vector
- Network
- Complexity
- High
- Privileges required
- None
- User interaction
- None
- Scope
- Unchanged
- Confidentiality
- High
- Integrity
- High
- Availability
- High