{"id":"EEF-CVE-2026-56813","summary":"Cookie attribute injection in Plug.Conn.Cookies.encode/2","details":"## Summary\n\nImproper Neutralization of Parameter/Argument Delimiters vulnerability in elixir-plug plug allows an attacker to inject or override HTTP cookie attributes.\n\nThe `Plug.Conn.Cookies.encode/2` function in `lib/plug/conn/cookies.ex` builds the `Set-Cookie` response header by interpolating the cookie value and its `path`, `domain`, `same_site`, and `extra` attributes directly into the header without neutralizing the `;` delimiter that separates cookie attributes.\n\nAn application that places attacker-controlled data into a cookie value or attribute (for example via `Plug.Conn.put_resp_cookie/4` when reflecting a username or preference) lets an attacker inject a `;` to append or override cookie attributes (such as `Domain` and `Path` scope, or dropping the `Secure` and `HttpOnly` flags), enabling cookie tossing and session fixation. Carriage return, line feed, and null bytes are rejected by `Plug.Conn` header validation, so HTTP response splitting is not possible, but attribute injection through `;` is not prevented.\n\nThis issue affects plug: from 0.1.0 before 1.16.6, from 1.17.0 before 1.17.4, from 1.18.0 before 1.18.5, from 1.19.1 before 1.19.5, and from 1.20.0 before 1.20.3.\n\n## Workarounds\n\nValidate or reject the `;` delimiter in any untrusted data before passing it as a cookie value or attribute to `Plug.Conn.put_resp_cookie/4` or `Plug.Conn.Cookies.encode/2`. Carriage return, line feed, and null bytes are already rejected by `Plug.Conn` header validation.","aliases":["CVE-2026-56813","GHSA-wpmj-jh88-rpgm"],"modified":"2026-09-24T21:45:02.546503158Z","published":"2026-07-10T12:51:08.758Z","database_specific":{"cwe_ids":["CWE-141"],"capec_ids":["CAPEC-61"],"cpe_ids":["cpe:2.3:a:elixir-plug:plug:*:*:*:*:*:*:*:*"]},"references":[{"type":"ADVISORY","url":"https://github.com/elixir-plug/plug/security/advisories/GHSA-wpmj-jh88-rpgm"},{"type":"WEB","url":"https://cna.erlef.org/cves/CVE-2026-56813.html"},{"type":"WEB","url":"https://github.com/elixir-plug/plug/commit/f26876aa67aaeb38e616638aa3efbcc2fe2906a5"},{"type":"FIX","url":"https://github.com/elixir-plug/plug/commit/3f00dfad4e20ba88472e315c90a25742bf178f8e"},{"type":"FIX","url":"https://github.com/elixir-plug/plug/commit/a6d1248659022749869963fd302687165ecf8c8b"},{"type":"FIX","url":"https://github.com/elixir-plug/plug/commit/4167981747fe9ce75f374b94a28861ae950ea992"},{"type":"FIX","url":"https://github.com/elixir-plug/plug/commit/149d9ed68fee0b4f77efd1e835ce5d785856697b"},{"type":"FIX","url":"https://github.com/elixir-plug/plug/commit/eceb8315ce9a31ef784943a95a8624ebd1bc7e06"},{"type":"PACKAGE","url":"https://hex.pm/packages/plug"}],"affected":[{"package":{"name":"plug","ecosystem":"Hex","purl":"pkg:hex/plug"},"ranges":[{"type":"SEMVER","events":[{"introduced":"0.1.0"},{"fixed":"1.16.6"}]},{"type":"SEMVER","events":[{"introduced":"1.17.0"},{"fixed":"1.17.4"}]},{"type":"SEMVER","events":[{"introduced":"1.18.0"},{"fixed":"1.18.5"}]},{"type":"SEMVER","events":[{"introduced":"1.19.1"},{"fixed":"1.19.5"}]},{"type":"SEMVER","events":[{"introduced":"1.20.0"},{"fixed":"1.20.3"}]}],"versions":["0.10.0","0.11.0","0.11.1","0.11.2","0.11.3","0.12.0","0.12.1","0.12.2","0.13.0","0.13.1","0.14.0","0.4.1","0.4.2","0.4.3","0.4.4","0.5.0","0.5.1","0.5.2","0.5.3","0.6.0","0.7.0","0.8.0","0.8.1","0.8.2","0.8.3","0.8.4","0.9.0","1.0.0","1.0.1","1.0.2","1.0.3","1.0.4","1.0.5","1.0.6","1.1.0","1.1.1","1.1.2","1.1.3","1.1.4","1.1.5","1.1.6","1.1.7","1.1.8","1.1.9","1.10.0","1.10.1","1.10.2","1.10.3","1.10.4","1.11.0","1.11.1","1.12.0","1.12.1","1.13.0","1.13.1","1.13.2","1.13.3","1.13.4","1.13.5","1.13.6","1.14.0","1.14.1","1.14.2","1.15.0","1.15.1","1.15.2","1.15.3","1.15.4","1.15.5","1.15.6","1.16.0","1.16.1","1.16.2","1.16.3","1.16.4","1.16.5","1.17.0","1.17.1","1.17.2","1.17.3","1.18.0","1.18.1","1.18.2","1.18.3","1.18.4","1.19.1","1.19.2","1.19.3","1.19.4","1.2.0","1.2.0-rc.0","1.2.1","1.2.2","1.2.3","1.2.4","1.2.5","1.2.6","1.20.0","1.20.1","1.20.2","1.3.0","1.3.1","1.3.2","1.3.3","1.3.4","1.3.5","1.3.6","1.4.0","1.4.0-rc.0","1.4.1","1.4.2","1.4.3","1.4.4","1.4.5","1.5.0","1.5.0-rc.0","1.5.0-rc.1","1.5.0-rc.2","1.5.1","1.6.0","1.6.1","1.6.2","1.6.3","1.6.4","1.7.0","1.7.1","1.7.2","1.8.0","1.8.1","1.8.2","1.8.3","1.9.0"],"database_specific":{"source":"https://cna.erlef.org/osv/EEF-CVE-2026-56813.json"}},{"ranges":[{"type":"GIT","repo":"https://github.com/elixir-plug/plug","events":[{"introduced":"f26876aa67aaeb38e616638aa3efbcc2fe2906a5"},{"fixed":"3f00dfad4e20ba88472e315c90a25742bf178f8e"},{"fixed":"a6d1248659022749869963fd302687165ecf8c8b"},{"fixed":"4167981747fe9ce75f374b94a28861ae950ea992"},{"fixed":"149d9ed68fee0b4f77efd1e835ce5d785856697b"},{"fixed":"eceb8315ce9a31ef784943a95a8624ebd1bc7e06"}]}],"database_specific":{"source":"https://cna.erlef.org/osv/EEF-CVE-2026-56813.json"}}],"schema_version":"1.9.0","severity":[{"type":"CVSS_V4","score":"CVSS:4.0/AV:L/AC:L/AT:P/PR:N/UI:N/VC:N/VI:L/VA:N/SC:N/SI:L/SA:N"}],"credits":[{"name":"Peter Ullrich","type":"FINDER"},{"name":"José Valim","type":"REMEDIATION_DEVELOPER"},{"name":"Jonatan Männchen / EEF","type":"ANALYST"}]}