CVE-2026-35611: Addressable has a Regular Expression Denial of Service in Addressable templates

Vulnerability summary

CVE-2026-35611 is a high (CVSS 7.5) vulnerability in addressable_project addressable. EPSS estimates a 0.36% chance of exploitation in the next 30 days, higher than 29.8% of scored vulnerabilities.

Timeline

1. 07-04-2026
   PublishedVulnerability first disclosed.
2. 09-04-2026
   Last modifiedVulnerability information updated.

Description

Addressable is an alternative implementation to the URI implementation that is part of Ruby's standard library. From 2.3.0 to before 2.9.0, within the URI template implementation in Addressable, two classes of URI template generate regular expressions vulnerable to catastrophic backtracking. Templates using the * (explode) modifier with any expansion operator (e.g., {foo*}, {+var*}, {#var*}, {/var*}, {.var*}, {;var*}, {?var*}, {&var*}) generate patterns with nested unbounded quantifiers that are O(2^n) when matched against a maliciously crafted URI. Templates using multiple variables with the + or # operators (e.g., {+v1,v2,v3}) generate patterns with O(n^k) complexity due to the comma separator being within the matched character class, causing ambiguous backtracking across k variables. When matched against a maliciously crafted URI, this can result in catastrophic backtracking and uncontrolled resource consumption, leading to denial of service. This vulnerability is fixed in 2.9.0.

• CWE-1333Inefficient Regular Expression ComplexityThe product uses a regular expression with a worst-case computational complexity that is inefficient and possibly exponential.