# CVE-2026-82617: Apache OpenNLP, Apache OpenNLP: ReDoS / stack exhaustion in RegexNameFinderFactory built-in EMAIL and URL patterns

> Attackers can cause denial of service via CPU exhaustion or stack overflow in Apache OpenNLP by submitting crafted text to built-in regex finders.

- **Severity:** Critical 10.0 (`CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:H/VI:H/VA:H/SC:H/SI:H/SA:H`)
- **Exploited in the wild:** Not known
- **Login needed:** Not needed
- **Attackable:** Over the internet
- **Victim action needed:** Not needed
- **Fix available:** Yes
- **Published:** 11 Sep 2026
- **Updated:** 11 Sep 2026
- **Also known as:** DEBIAN-CVE-2026-82617, GHSA-f3wj-w3qw-rw57, UBUNTU-CVE-2026-82617

## What is CVE-2026-82617?

CVE-2026-82617 is a critical denial of service vulnerability in Apache OpenNLP, published on 11 Sep 2026. An attacker can exploit it over the internet without logging in, with no action from the victim.

### Official description

The two built-in name-finder patterns exposed by
opennlp.tools.namefind.RegexNameFinderFactory - DEFAULT_REGEX_NAME_FINDER.EMAIL
and DEFAULT_REGEX_NAME_FINDER.URL - contain ambiguous nested quantifiers. An
application that obtains these finders through
RegexNameFinderFactory.getDefaultRegexNameFinders(...) and then applies them to
untrusted text through RegexNameFinder.find(String[]) or RegexNameFinder.find(String)
can be driven into super-linear backtracking or into unbounded matcher recursion by a
small crafted input.

For the EMAIL pattern, a long run of local-part characters that is never followed by an
@ forces the matcher to re-scan to end-of-input from every starting offset. Cost grows
quadratically with input length: an input of approximately 32 KB consumes several seconds
of CPU in a single find() call and returns no match, and each doubling of the input
multiplies the cost roughly four-fold.

For the URL pattern, the query-string sub-expression nests a capturing repetition inside
an outer repetition. The JDK matcher recurses once per query token, so an input of
approximately 4 KB containing many &-separated tokens exhausts the thread stack and
causes java.lang.StackOverflowError to propagate out of find(), terminating the
calling thread. On a thread created with a smaller stack (for example -Xss512k, typical
of server worker pools) approximately 1 KB is sufficient.

In both cases an attacker who can supply text for analysis can convert a single request
into seconds to minutes of pinned CPU, or into an abrupt thread death, denying service to
the embedding application. No authentication, special configuration, or model file is
required beyond the application having selected one of the two built-in finders.

This issue affects Apache OpenNLP: from 2.0.0 through 2.5.11; from 3.0.0-M1 through
3.0.0-M5.

Users are recommended to upgrade to version 2.5.12, or to 3.0.0-M6 for users tracking the
3.0.0 milestone line, which fix the issue.

Weakness: CWE-1333 (Inefficient Regular Expression Complexity)

## Which versions are affected by CVE-2026-82617?

It affects 1 product.


Products: Apache Opennlp.

## How do I fix CVE-2026-82617?

Upgrade to a fixed version.

## Is CVE-2026-82617 being exploited?

There is no known exploitation of CVE-2026-82617 in the wild and no public exploit code.

## Other vulnerabilities in Apache OpenNLP

- [CVE-2026-42027](https://insights.sbomify.com/CVE-2026-42027/): Apache OpenNLP: Arbitrary Class Instantiation via Model Manifest in ExtensionLoader (critical 9.8)
- [CVE-2017-12620](https://insights.sbomify.com/CVE-2017-12620/): Improper Restriction of XML External Entity Reference in Apache OpenNLP (critical 9.8)
- [CVE-2026-40682](https://insights.sbomify.com/CVE-2026-40682/): Apache OpenNLP: XXE via Dictionary Parsing in DictionaryEntryPersistor (critical 9.1)
- [CVE-2026-67211](https://insights.sbomify.com/CVE-2026-67211/): Apache OpenNLP: OOM DoS via Unbounded Array Allocation in SymSpellModelSerializer (high 7.5)
- [CVE-2026-42440](https://insights.sbomify.com/CVE-2026-42440/): Apache OpenNLP: OOM DoS via Unbounded Array Allocation in AbstractModelReader (high 7.5)

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-82617 and fix it if it is affected.

What it is: CVE-2026-82617 is a critical denial of service vulnerability in Apache OpenNLP, published on 11 Sep 2026. An attacker can exploit it over the internet without logging in, with no action from the victim.
Exploitation: There is no known exploitation of CVE-2026-82617 in the wild and no public exploit code.

Affected product: Apache OpenNLP. 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-2026-82617/ (Markdown: https://insights.sbomify.com/CVE-2026-82617/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-82617
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-82617
- OSV: https://osv.dev/vulnerability/CVE-2026-82617

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-82617/
Summaries are generated and may contain mistakes; the official description above is the record.