The vulnerability in Erlang/OTP public_key certificate path validation arises because the certificate policy tree maintained during RFC 5280 policy processing grows without an upper bound. Specifically, the functions pubkey_policy_tree:add_leaves/2 and pubkey_policy_tree:add_leaf_siblings/2 extend the policy tree per policy per certificate, causing exponential growth (on the order of M^K nodes for M policies per certificate and K certificates). An attacker can exploit this by presenting a crafted X.509 certificate chain during the TLS handshake, causing resource exhaustion that pins BEAM schedulers and exhausts memory, resulting in denial of service of the Erlang VM. This vulnerability affects OTP versions from 26.2 up to but not including 29.0.4, 28.5.0.4, and 27.3.4.15, and the corresponding public_key versions prior to 1.21.4, 1.20.3.4, and 1.17.1.5.

Exploitation leads to denial of service by exhausting CPU and memory resources of the Erlang VM, potentially causing the entire VM to become unresponsive. The attacker only needs to present a crafted certificate chain during a TLS handshake, which is a normal part of TLS communication, making any incoming or outgoing TLS connection that validates peer certificates vulnerable.

Patch status is not yet confirmed — check the vendor advisory for current remediation guidance. The vulnerability affects specific OTP and public_key versions as stated. Until a patch or official fix is confirmed, consider restricting or validating incoming certificate chains to limit policy complexity if possible. Monitor vendor advisories for updates and apply official patches once available.