# CVE-2026-87721: Denial of Service via Exponential Backtracking in ANTLR Search Query Parser in Gerrit Code Review

> Unauthenticated attackers can cause persistent denial of service in Gerrit Code Review by sending crafted search queries that exhaust CPU and worker threads.

- **Severity:** High 8.7 (`CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:N/VI:N/VA:H/SC:N/SI:N/SA:N`)
- **Exploited in the wild:** Not known
- **Login needed:** Not needed
- **Attackable:** Over the internet
- **Victim action needed:** Not needed
- **Fix available:** No
- **Published:** 24 Sep 2026
- **Updated:** 25 Sep 2026
- **Also known as:** GHSA-q3rp-qmhw-57f7

## What is CVE-2026-87721?

CVE-2026-87721 is a high-severity denial of service vulnerability in Gerrit, published on 24 Sep 2026. An attacker can exploit it over the internet without logging in, with no action from the victim.

### Official description

Uncontrolled Resource Consumption (CWE-400 / CWE-407) in the ANTLR 3 search query parser (QueryParser / Query.g) in Gerrit Code Review versions 2.0.19 through 3.12.9, 3.13.0 through 3.13.8, and 3.14.0 through 3.14.2 allows an unauthenticated remote attacker (or an authenticated user if anonymous read access is disabled) to cause a persistent denial of service (CPU exhaustion and HTTP worker thread pool starvation requiring a server restart) via crafted search queries containing deeply nested parentheses sent to query evaluation endpoints (/changes/?q=, /accounts/?q=, /groups/?query=, /projects/?query=, /Documentation/?q=, /changes/{id}/query?expression=, or SSH gerrit query). Because syntactic predicates in conditionOr and conditionAnd recurse via conditionBase without memoization prior to capability or visibility checks and worker threads do not abort when the client disconnects, a small number of requests (such as 25 requests matching default httpd.maxThreads) can permanently pin all HTTP worker threads. This issue is fixed in Gerrit Code Review versions 3.12.10, 3.13.9, and 3.14.3.

Weakness: CWE-834 (Excessive Iteration), CWE-407 (Inefficient Algorithmic Complexity), CWE-400 (Uncontrolled Resource Consumption)

## Which versions are affected by CVE-2026-87721?


## How do I fix CVE-2026-87721?

No fix has been published for CVE-2026-87721 yet. Limit exposure of the affected software until one is available.

## Is CVE-2026-87721 being exploited?

It is not confirmed as exploited in the wild, but public exploit code for CVE-2026-87721 exists.

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-87721 and fix it if it is affected.

What it is: CVE-2026-87721 is a high-severity denial of service vulnerability in Gerrit, published on 24 Sep 2026. An attacker can exploit it over the internet without logging in, with no action from the victim.
Exploitation: It is not confirmed as exploited in the wild, but public exploit code for CVE-2026-87721 exists.

Affected product: Gerrit. No package-level version data is available, so check the vendor advisory linked from the reference page.

Task:
1. Search the dependency manifests and lockfiles (for example package.json, package-lock.json, requirements.txt, poetry.lock, uv.lock, pom.xml, build.gradle, go.mod, Cargo.lock, Gemfile.lock) and any Dockerfiles for the affected packages, including transitive dependencies.
2. If an affected version is in use, upgrade it to the fixed version for its release line with the project's package manager, so the lockfile is regenerated. Prefer the smallest upgrade that fixes it.
3. If there is no fix, or the upgrade would break the build, do not guess: explain the risk and the safest workaround instead.
4. Run the tests and summarise what changed and why.
5. If nothing in the project is affected, say so and change nothing.

Reference: https://insights.sbomify.com/CVE-2026-87721/ (Markdown: https://insights.sbomify.com/CVE-2026-87721/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-87721
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-87721
- OSV: https://osv.dev/vulnerability/CVE-2026-87721

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-87721/
Summaries are generated and may contain mistakes; the official description above is the record.