CVE-2026-37227 Overview
CVE-2026-37227 affects FlexRIC v2.0.0, an Open RAN near real-time RAN Intelligent Controller (near-RT RIC) developed by EURECOM. The vulnerability resides in stub message handlers that process whitelisted but unimplemented E2 Application Protocol (E2AP) message types. A remote unauthenticated attacker can send a decodable E2AP Protocol Data Unit (PDU), such as E2nodeConfigurationUpdate, to the near-RT RIC listening on port 36421. The handler invokes an unconditional assert(0), terminating the process with SIGABRT and producing a denial-of-service condition.
Critical Impact
Unauthenticated network attackers can crash the FlexRIC near-RT RIC process by transmitting a single valid E2AP message, disrupting Open RAN control-plane operations.
Affected Products
- FlexRIC v2.0.0 (EURECOM mosaic5g)
- Near-RT RIC component listening on TCP/SCTP port 36421
- Deployments using E2AP stub message handlers for unimplemented message types
Discovery Timeline
- 2026-06-01 - CVE-2026-37227 published to NVD
- 2026-06-01 - Last updated in NVD database
Technical Details for CVE-2026-37227
Vulnerability Analysis
FlexRIC implements the E2AP protocol to interface between the near-RT RIC and E2 nodes such as gNBs. Several E2AP message types pass the inbound whitelist validation but lack production handlers. The stub handlers contain an unconditional assert(0) statement intended as a developer placeholder. When the assertion fires in a release build linked against an assert implementation that aborts, the process receives SIGABRT and terminates. The flaw is classified under [CWE-617] Reachable Assertion.
The attack requires no authentication and no user interaction. An attacker reaching the RIC's E2AP port can transmit a single well-formed PDU to trigger termination. The impact is limited to availability, but the near-RT RIC is a central control-plane component, so a crash disrupts RAN intelligent control workflows including xApp execution and E2 node coordination.
Root Cause
The root cause is the use of assert(0) as a placeholder inside reachable code paths for whitelisted message types. Whitelist validation permits the message to reach the handler, but the handler does not gracefully reject or ignore the PDU. Instead, it asserts and aborts. Input that should produce a controlled error response produces an unrecoverable crash.
Attack Vector
The attacker establishes a connection to the near-RT RIC's E2AP endpoint on port 36421. The attacker constructs a valid ASN.1-encoded E2AP PDU of a whitelisted but unimplemented type, such as E2nodeConfigurationUpdate. Upon receipt, the RIC decodes the message, routes it to the stub handler, executes the assert(0), and terminates via SIGABRT. No prior session state, authentication, or specific xApp configuration is required.
No verified public exploit code is available. Technical details are documented in the GitHub Security Advisory.
Detection Methods for CVE-2026-37227
Indicators of Compromise
- Unexpected SIGABRT termination of the FlexRIC near-RT RIC process with core dumps referencing E2AP stub handler functions
- Repeated crash-restart cycles of the RIC process following inbound traffic on port 36421
- Log entries indicating receipt of E2nodeConfigurationUpdate or similar whitelisted-but-unimplemented E2AP message types immediately preceding process exit
Detection Strategies
- Monitor process supervisors and systemd journals for abnormal exit codes from the near-RT RIC binary
- Inspect SCTP and TCP flows targeting port 36421 from non-allowlisted E2 node sources
- Correlate RIC process restarts with packet captures showing E2AP PDUs of unimplemented message types
Monitoring Recommendations
- Enable core dump collection and stack trace logging for the FlexRIC near-RT RIC process to confirm assertion-driven aborts
- Deploy network telemetry on the E2 interface to baseline expected E2AP message types and flag anomalies
- Alert on repeated SCTP associations from the same peer followed by RIC service restarts within short time windows
How to Mitigate CVE-2026-37227
Immediate Actions Required
- Restrict network reachability to port 36421 so only authorized E2 nodes can establish E2AP sessions with the near-RT RIC
- Place the near-RT RIC behind segmented management networks and enforce ACLs at the host and network layer
- Monitor the FlexRIC GitLab repository for upstream patches that replace assert(0) stubs with safe rejection logic
Patch Information
No vendor patch is referenced in the NVD entry at publication. Track the upstream FlexRIC GitLab repository and the GitHub Security Advisory for fix availability. Until a patched release is available, operators should apply compensating controls.
Workarounds
- Filter inbound E2AP PDUs at a network proxy or middlebox to drop message types known to trigger stub handlers, including E2nodeConfigurationUpdate
- Build FlexRIC with NDEBUG defined only after auditing that disabling assertions does not introduce undefined behavior in dependent code paths
- Wrap the near-RT RIC under a process supervisor configured for rapid restart while logging crash artifacts for forensic review
- Limit exposure of the E2 interface to trusted lab or operator-controlled networks until a vendor fix is released
Disclaimer: This content was generated using AI. While we strive for accuracy, please verify critical information with official sources.
