EXPOSURES › CVE-2026-82617
CVE-2026-82617
CRITICALAmbiguous regex patterns in Apache OpenNLP cause quadratic CPU consumption or stack overflows on untrusted input.
CVE-2026-82617 exposes super-linear backtracking and unbounded recursion in Apache OpenNLP's built-in name-finder regexes, leading to severe CPU exhaustion or thread termination on crafted inputs. DIB orgs must audit untrusted text processing pipelines for similar regex vulnerabilities, as they can degrade system performance or crash services without requiring remote code execution. The flaw is avoidable through proper regex design and input validation.
Shame score — A critical CVSS 9.8 flaw in a widely used open-source library that causes denial-of-service via resource exhaustion, but lacks remote code execution or data breach implications.
▸ RECOMMENDED ACTION Critical severity — schedule patching of the affected products.
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.