Bouncy Castle Java CVE-2026-59645

Exploitation requires that the target application uses Bouncy Castle's OERInputStream to parse IEEE 1609.2 or ETSI TS 103 097 V2X message structures from attacker-controlled input, and that this parsing occurs before signature verification - which is the standard operational flow in the affected library. Applications specifically configured to receive and decode V2X messages from untrusted sources (V2X PKI enrollment authorities, roadside units, certificate management systems, DSRC/C-V2X receivers) are directly vulnerable with no additional preconditions. The CVSS vector (AV:N/AC:L/PR:N/UI:N) confirms no authentication and no complex preconditions. Limiting factors: applications that only process OER data from sources they have already authenticated via an out-of-band trust mechanism face substantially reduced exposure; applications that do not call the OER parser at all (i.e., do not use Bouncy Castle for IEEE 1609.2 message parsing) are entirely unaffected regardless of which Bouncy Castle version they run.

The CVSS 4.0 score of 8.7 (AV:N/AC:L/AT:N/PR:N/UI:N/VA:H) accurately characterises the threat: network-reachable, unauthenticated, low complexity, high availability impact, no confidentiality or integrity effect. This is not a high-CVSS-but-low-real-risk case - the combination of no required authentication, pre-verification reachability, and a small crafted payload (few KB) makes exploitation straightforward for any attacker who can deliver OER data to a vulnerable endpoint. EPSS score is not included in the available intelligence and cannot be assessed. This CVE is not currently listed in the CISA KEV catalog - no confirmed active exploitation at time of analysis. No public exploit code has been identified, though the detailed patch commit provides sufficient implementation detail for a researcher to reproduce all three DoS vectors. Real-world risk is concentrated in V2X infrastructure, automotive PKI systems, roadside units, and on-board units that process untrusted IEEE 1609.2 messages; general-purpose Java applications that do not use OER parsing are unaffected. For in-scope deployments, this is a genuine priority: a small crafted message can crash the parsing JVM with no privileges required.

An unauthenticated remote attacker sends a few kilobytes of crafted IEEE 1609.2 OER-encoded data - with a self-referential Ieee1609Dot2Data structure nested inside its own SignedData payload - to any network-exposed endpoint that passes untrusted input to Bouncy Castle's OERInputStream before signature verification. The parser enters unbounded recursive descent across the cyclic schema, exhausting the JVM thread stack and throwing StackOverflowError, which crashes the parsing thread or the entire JVM process. No public exploit code has been identified at time of analysis, but the patch commit's release notes describe the attack precisely and provide sufficient detail to reproduce it.