CVE-2026-35611 — addressable
HIGHCVE-2026-35611 is a high-severity (CVSS 7.5) CWE-1333 vulnerability in addressable. A fix is available for addressable — see the affected versions and patch details below.
Addressable has a Regular Expression Denial of Service in Addressable templates
Exploitation Status
No confirmed exploitation observed yet
- CISA assesses this as automatable — exploitation doesn’t require manual, per-target effort, which raises the odds of mass scanning and opportunistic attacks.
- CISA’s own triage has not observed active exploitation or public proof-of-concept code for this CVE as of its last assessment.
Exploitation and automatability from CISA’s SSVC triage for CVE-2026-35611.
EPSS Exploitation Probability
Probability of exploitation in the next 30 days, from FIRST.org EPSS.
How urgent is this, really
Where this sits among everything scored
Real-World Exposure
addressableReal-time download stats are indexed for npm and PyPI packages. This vulnerability affects RubyGems packages — download data is not available via public APIs for these ecosystems.
Description
Impact
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. The first pattern was partially addressed in 2.8.10 for certain operator combinations. Both patterns are fully remediated in 2.9.0.
Users of the URI parsing capabilities in Addressable but not the URI template matching capabilities are unaffected.
Affected Versions
This vulnerability affects Addressable >= 2.3.0 (note: 2.3.0 and 2.3.1 were yanked; the earliest installable release is 2.3.2). It was partially fixed in version 2.8.10 and fully remediated in 2.9.0.
The vulnerability is more exploitable on MRI Ruby < 3.2 and on all versions of JRuby and TruffleRuby. MRI Ruby 3.2 and later ship with Onigmo 6.9, which introduces memoization that prevents catastrophic backtracking for the first class of template. JRuby and TruffleRuby do not implement equivalent memoization and remain vulnerable to all patterns.
This has been confirmed on the following runtimes:
| Runtime | Status |
|---|---|
| MRI Ruby 2.6 | Vulnerable |
| MRI Ruby 2.7 | Vulnerable |
| MRI Ruby 3.0 | Vulnerable |
| MRI Ruby 3.1 | Vulnerable |
| MRI Ruby 3.2 | Partially vulnerable |
| MRI Ruby 3.3 | Partially vulnerable |
| MRI Ruby 3.4 | Partially vulnerable |
| MRI Ruby 4.0 | Partially vulnerable |
| JRuby 10.0 | Vulnerable |
| TruffleRuby 21.2 | Vulnerable |
Workarounds
-
Upgrade to MRI Ruby 3.2 or later, if your application does not use JRuby or TruffleRuby. The Onigmo memoization introduced in MRI Ruby 3.2 prevents catastrophic backtracking from nested unbounded quantifiers (pattern 1 above — templates using the
*modifier). It does not reliably mitigate the O(n^k) multi-variable case (pattern 2), so upgrading Ruby alone may not be sufficient if your templates use{+v1,v2,...}or{#v1,v2,...}syntax. -
Avoid using vulnerable template patterns when matching user-supplied input on unpatched versions of the library:
- Templates using the
*(explode) modifier:{foo*},{+var*},{#var*},{.var*},{/var*},{;var*},{?var*},{&var*} - Templates using multiple variables with the
+or#operators:{+v1,v2},{#v1,v2,v3}, etc.
- Templates using the
-
Apply a short timeout around any call to
Template#matchorTemplate#extractthat processes user-supplied data.
References
- https://owasp.org/www-community/attacks/Regular_expression_Denial_of_Service_-_ReDoS
- https://cwe.mitre.org/data/definitions/1333.html
- https://www.regular-expressions.info/catastrophic.html
Credits
Discovered in collaboration with @jamfish.
For more information
If you have any questions or comments about this advisory:
Affected Packages
| Ecosystem | Package | Vulnerable range | Fix |
|---|---|---|---|
| 💎RubyGems | addressable | ≥ 2.3.0&&< 2.9.0 | 2.9.0bundle update addressable --conservative |
Affected Products
addressableaddressable_projectDetection & mitigation playbook
Open-source dependencyDetect
Scan your dependency tree (package-lock.json, pnpm-lock.yaml, requirements.txt, go.sum, etc.) for addressable, including transitive dependencies — a direct dependency you never call can still pull in a vulnerable version.
Fix
Update addressable to 2.9.0 or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms CVE-2026-35611 is resolved across your whole dependency graph.
Workarounds
Cap what an attacker can consume: apply request size, rate and timeout limits in front of the affected component, and run it with memory and CPU limits so exhaustion degrades one worker rather than the whole service.
Fixing This On Your OS
If you run this on a Linux distribution, patch through your package manager against the distro's own security advisory below — it tracks the exact backported fix for your release, which can ship on a different timeline (and sometimes a different severity) than the upstream project.
Mitigation for this issue is either not available or the currently available options do not meet the Red Hat Product Security criteria comprising ease of use and deployment, applicability to widespread installation base, or stability.Source: Red Hat security advisory for CVE-2026-35611 (CC BY 4.0)
Frequently Asked Questions
Is CVE-2026-35611 in your dependencies?
Find it across RubyGems, including transitive dependencies.