{"id":"CVE-2021-40523","aliases":["EUVD-2021-27699","GHSA-9rqj-h33r-qgm8"],"status":"published","title":"In Contiki 3.0, Telnet option negotiation is mishandled. During negotiation between a server and...","description":"In Contiki 3.0, Telnet option negotiation is mishandled. During negotiation between a server and a client, the server may fail to give the WILL/WONT or DO/DONT response for DO and WILL commands because of improper handling of exception condition, which leads to property violations and denial of service. Specifically, a server sometimes sends no response, because a fixed buffer space is available for all responses and that space may have been exhausted.","severity":{"version":"3.1","score":7.5,"vector":"CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H","level":"high","assessor":"primary","from":"nvd"},"epss":{"day":"2026-11-09","score":0.00961,"percentile":0.61821,"model":"v2026.06.15"},"facts":{"in_kev":false,"known_exploited":false,"public_exploit":false,"fix_available":false},"cwes":["CWE-754"],"published":"2021-09-05T18:26:43Z","modified":"2026-06-17T04:07:05Z","products":[{"vendor":"contiki-os","product":"contiki"}],"references":[{"url":"https://github.com/contiki-os/contiki/issues/2686","tags":["x_refsource_MISC","x_transferred","Patch","Third Party Advisory"]},{"url":"https://nvd.nist.gov/vuln/detail/CVE-2021-40523"},{"url":"https://github.com/advisories/GHSA-9rqj-h33r-qgm8"}],"sources":{"cve":[{"id":"CVE-2021-40523","description":"In Contiki 3.0, Telnet option negotiation is mishandled. During negotiation between a server and a client, the server may fail to give the WILL/WONT or DO/DONT response for DO and WILL commands because of improper handling of exception condition, which leads to property violations and denial of service. Specifically, a server sometimes sends no response, because a fixed buffer space is available for all responses and that space may have been exhausted.","status":"published","published":"2021-09-05T18:26:43Z","modified":"2024-08-04T02:44:10.79Z","updated_at":"2026-11-02T14:33:01.495293Z"}],"euvd":[{"id":"EUVD-2021-27699","description":"In Contiki 3.0, Telnet option negotiation is mishandled. During negotiation between a server and a client, the server may fail to give the WILL/WONT or DO/DONT response for DO and WILL commands because of improper handling of exception condition, which leads to property violations and denial of service. Specifically, a server sometimes sends no response, because a fixed buffer space is available for all responses and that space may have been exhausted.","status":"published","published":"2021-09-05T18:26:43Z","modified":"2024-08-04T02:44:10Z","updated_at":"2026-11-03T03:24:20.264881Z"}],"ghsa":[{"id":"GHSA-9rqj-h33r-qgm8","title":"In Contiki 3.0, Telnet option negotiation is mishandled. During negotiation between a server and...","description":"In Contiki 3.0, Telnet option negotiation is mishandled. During negotiation between a server and a client, the server may fail to give the WILL/WONT or DO/DONT response for DO and WILL commands because of improper handling of exception condition, which leads to property violations and denial of service. Specifically, a server sometimes sends no response, because a fixed buffer space is available for all responses and that space may have been exhausted.","status":"published","published":"2022-05-24T19:13:01Z","modified":"2023-01-30T05:01:54Z","cwes":["CWE-754"],"updated_at":"2026-11-02T14:46:30.744651Z"}],"nvd":[{"id":"CVE-2021-40523","description":"In Contiki 3.0, Telnet option negotiation is mishandled. During negotiation between a server and a client, the server may fail to give the WILL/WONT or DO/DONT response for DO and WILL commands because of improper handling of exception condition, which leads to property violations and denial of service. Specifically, a server sometimes sends no response, because a fixed buffer space is available for all responses and that space may have been exhausted.","status":"published","published":"2021-09-05T19:15:15.03Z","modified":"2026-06-17T04:07:05.043Z","cvss":[{"version":"3.1","score":7.5,"vector":"CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H","level":"high","assessor":"primary"},{"version":"2.0","score":5,"vector":"AV:N/AC:L/Au:N/C:N/I:N/A:P","level":"medium","assessor":"primary"}],"cwes":["CWE-754"],"updated_at":"2026-11-02T14:06:58.05696Z"}]}}