CVE-2026-82617: Apache OpenNLP, Apache OpenNLP: ReDoS / stack exhaustion in RegexNameFinderFactory built-in EMAIL and URL patterns
The two built-in name-finder patterns exposed by opennlp.tools.namefind.RegexNameFinderFactory - DEFAULTREGEXNAMEFINDER.EMAIL and DEFAULTREGEXNAMEFINDER.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.
Affected Software
Remediation
Recommended actions to resolve this vulnerability, in priority order.
- Upgrade
Upgrade
Apache OpenNLPto a version that resolves this vulnerability.Fixed in 2.5.12 - Upgrade
Upgrade
Apache OpenNLPto a version that resolves this vulnerability.Fixed in 3.0.0-M6
Event History
Frequently Asked Questions
Which applications are exposed?
Applications are exposed when they obtain the built-in EMAIL or URL finders through RegexNameFinderFactory.getDefaultRegexNameFinders(...) and apply them to untrusted text using RegexNameFinder.find(String[]) or RegexNameFinder.find(String).
What input is needed to trigger the issue?
For the EMAIL pattern, a long sequence of local-part characters with no following @ causes repeated scans to the end of the input. For the URL pattern, an input with many &-separated query-string tokens can drive recursive matcher calls until the thread stack is exhausted.
How might exploitation appear in production?
EMAIL-pattern processing can consume several seconds of CPU for an approximately 32 KB input while returning no match, with processing cost growing roughly four-fold when input length doubles. URL-pattern processing can terminate with java.lang.StackOverflowError for an approximately 4 KB input containing many query tokens.