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CVE-2026-129456

CVE-2026-129456

What's the vulnerability?

In FRRouting, bgpd accepts a Tunnel Encapsulation attribute (type 23) whose outer TLV length does not match the length of the attribute: the mismatch is only logged and the attribute is processed anyway. A BGP neighbor can send UPDATE messages carrying such an attribute that put the reference count of the attribute's interned sub-TLV chain out of balance, so that the chain is freed while routes stored by bgpd (Adj-RIB-In entries and RIB paths) still point to it. When those routes are later replaced, withdrawn or cleared, for example when the session goes down, bgpd reads the freed memory, decrements a reference count inside it and frees it a second time. In the reporter's build without AddressSanitizer this ended in an assertion failure in bgpd's memory accounting, aborting bgpd and dropping all BGP sessions on the router, and the neighbor can repeat it each time bgpd restarts. Because freed heap memory is written to and freed again, consequences beyond a crash cannot be ruled out. An established BGP session is required. bgpd processes attribute 23 from every neighbor, including eBGP neighbors, unless it is explicitly discarded, although RFC 9012 requires it to be filtered on eBGP sessions by default. The issue was reproduced with "soft-reconfiguration inbound" configured for the neighbor, and the reporter observed that the crash does not occur on every attempt.

R4IM analyst take

Business impact & how R4IM helps

This advisory is on our active-exploitation watchlist. Attackers are using it for initial access, privilege escalation or lateral movement in real-world intrusions. R4IM's offensive security and SOC teams already have detections, exploit replicas and remediation playbooks for this issue.

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Prove it with a pentest

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If the affected product is internet-facing, our AppSec team will harden it against this and related OWASP-class issues.

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Recommended remediation

  1. Inventory all assets running the affected vendor and product, including shadow IT and third-party hosted instances.
  2. Apply the vendor patch or mitigation referenced in the advisories below. Where no patch exists, isolate the asset or restrict network exposure.
  3. Hunt for indicators of prior compromise — exploitation of this class of bug often predates public disclosure.
  4. Deploy detections for the exploit primitives (network signature, EDR rule, WAF rule) and re-test after remediation.

Need help executing these steps? Our team typically completes validation and remediation within a single patch cycle. Request remediation support →

Vendor & research references