{"cve":"CVE-2026-65623","nvd":{"published":"2026-07-24T17:17:34.107","modified":"2026-10-24T13:10:00.147","status":"Awaiting Analysis","description":"Inefficient Algorithmic Complexity vulnerability in mtrudel bandit allows unauthenticated remote denial of service via CPU exhaustion during WebSocket fragment reassembly.\n\nThe size guard 'Elixir.Bandit.WebSocket.Connection':oversize_message?/2 called from handle_frame/3 in lib/bandit/websocket/connection.ex appends each non-final continuation frame to a left-nested iolist and then re-measures the entire accumulated buffer with IO.iodata_length/1 on every frame. Because the buffer grows by one element per frame and is fully re-traversed each time, reassembly work is quadratic (O(n^2)) in the number of continuation frames.\n\nThe max_fragmented_message_size limit (default 8 MB) bounds total bytes but not frame count, and each frame can carry as little as one payload byte, so an attacker can send millions of tiny continuation frames using modest bandwidth to pin a CPU core for minutes to hours. Many concurrent connections can starve the whole server of CPU, denying service to legitimate users. The WebSocket read timeout does not help, because it is an idle timeout evaluated between reads and cannot preempt the synchronous reassembly work spent inside a single callback.\n\nThis issue affects bandit: from 1.11.0 before 1.12.1.","cvss_v4":{"vector":"CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:N/VI:N/VA:H/SC:N/SI:N/SA:N","score":8.7},"cvss_v3":null,"cwes":["CWE-407"],"references":["https://cna.erlef.org/cves/CVE-2026-65623.html","https://github.com/mtrudel/bandit/commit/418ef7e906192a230ddba112f7a669c87b6b0e3a","https://github.com/mtrudel/bandit/security/advisories/GHSA-vg8x-66vg-5pxh","https://osv.dev/vulnerability/EEF-CVE-2026-65623","https://github.com/mtrudel/bandit/security/advisories/GHSA-vg8x-66vg-5pxh"],"products":[],"source":"nvd","synced_at":"2026-10-24T16:53:27.712498749+00:00"},"epss":{"cve":"CVE-2026-65623","score":0.0048,"percentile":0.41135,"date":"2026-10-25"},"kev":null,"osv":[],"attribution":["This product uses the NVD API but is not endorsed or certified by the NVD.","EPSS scores: FIRST Exploit Prediction Scoring System, https://www.first.org/epss","Known exploited vulnerabilities: CISA Known Exploited Vulnerabilities Catalog, https://www.cisa.gov/known-exploited-vulnerabilities-catalog","Package advisories: OSV (https://osv.dev), from the GitHub Advisory Database, PyPA, Go, RustSec and other ecosystem databases, under CC-BY 4.0 or CC0","CVE records: the CVE Program's CVE List (https://www.cve.org), under its terms of use (https://www.cve.org/Legal/TermsOfUse). CVE is a registered trademark of The MITRE Corporation; this product is not affiliated with the CVE Program."]}