{"id":"CVE-2021-43838","aliases":["EUVD-2021-2445","GHSA-55xv-f85c-248q"],"status":"published","title":"Regular Expression Denial of Service (ReDoS) in jsx-slack","description":"jsx-slack is a library for building JSON objects for Slack Block Kit surfaces from JSX. In versions prior to 4.5.1 users are vulnerable to a regular expression denial-of-service (ReDoS) attack. If attacker can put a lot of JSX elements into `\u003cblockquote\u003e` tag, an internal regular expression for escaping characters may consume an excessive amount of computing resources. jsx-slack v4.5.1 has patched to a regex for escaping blockquote characters. Users are advised to upgrade as soon as possible.","severity":{"version":"3.1","score":5.3,"vector":"CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:L","level":"medium","assessor":"cna","from":"cve"},"epss":{"day":"2026-11-10","score":0.01422,"percentile":0.73091,"model":"v2026.06.15"},"facts":{"in_kev":false,"known_exploited":false,"public_exploit":false,"fix_available":true},"cwes":["CWE-1333","CWE-400"],"published":"2021-12-17T18:20:11Z","modified":"2026-10-20T10:55:04Z","fixes":[{"ecosystem":"npm","package":"jsx-slack","fixed_in":["4.5.1"],"sources":["ghsa","osv"]}],"affected":[{"source":"ghsa","ecosystem":"npm","package":"jsx-slack","ranges":[{"type":"ECOSYSTEM","events":[{"introduced":"0"},{"fixed":"4.5.1"}]}]},{"source":"osv","ecosystem":"npm","package":"jsx-slack","ranges":[{"type":"SEMVER","events":[{"introduced":"0"},{"fixed":"4.5.1"}]}]}],"products":[{"vendor":"jsx-slack_project","product":"jsx-slack"},{"vendor":"yhatt","product":"jsx-slack"}],"references":[{"url":"https://github.com/yhatt/jsx-slack/security/advisories/GHSA-55xv-f85c-248q","tags":["x_refsource_CONFIRM","x_transferred","Exploit","Patch","Third Party Advisory","fix","web"]},{"url":"https://github.com/yhatt/jsx-slack/commit/36e4a10405e4c7745333e245fcc5029c02c7065d","tags":["x_refsource_MISC","x_transferred","Patch","Third Party Advisory","fix","web"]},{"url":"https://nvd.nist.gov/vuln/detail/CVE-2021-43838","tags":["advisory"]},{"url":"https://github.com/advisories/GHSA-55xv-f85c-248q"},{"url":"https://github.com/yhatt/jsx-slack","tags":["web"]}],"sources":{"cve":[{"id":"CVE-2021-43838","title":"Regular Expression Denial of Service (ReDoS) in jsx-slack","description":"jsx-slack is a library for building JSON objects for Slack Block Kit surfaces from JSX. In versions prior to 4.5.1 users are vulnerable to a regular expression denial-of-service (ReDoS) attack. If attacker can put a lot of JSX elements into `\u003cblockquote\u003e` tag, an internal regular expression for escaping characters may consume an excessive amount of computing resources. jsx-slack v4.5.1 has patched to a regex for escaping blockquote characters. Users are advised to upgrade as soon as possible.","status":"published","published":"2021-12-17T18:20:11Z","modified":"2024-08-04T04:10:16.268Z","cvss":[{"version":"3.1","score":5.3,"vector":"CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:L","level":"medium","assessor":"cna"}],"cwes":["CWE-400"],"updated_at":"2026-11-02T14:32:56.689433Z"}],"euvd":[{"id":"EUVD-2021-2445","description":"jsx-slack is a library for building JSON objects for Slack Block Kit surfaces from JSX. In versions prior to 4.5.1 users are vulnerable to a regular expression denial-of-service (ReDoS) attack. If attacker can put a lot of JSX elements into `\u003cblockquote\u003e` tag, an internal regular expression for escaping characters may consume an excessive amount of computing resources. jsx-slack v4.5.1 has patched to a regex for escaping blockquote characters. Users are advised to upgrade as soon as possible.","status":"published","published":"2021-12-17T18:20:11Z","modified":"2024-08-04T04:10:16Z","cvss":[{"version":"3.1","score":5.3,"vector":"CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:L","level":"medium"}],"updated_at":"2026-11-03T03:24:13.193734Z"}],"ghsa":[{"id":"GHSA-55xv-f85c-248q","title":"Regular Expression Denial of Service (ReDoS) in jsx-slack","description":"jsx-slack v4.5.1 and earlier versions are vulnerable to a regular expression denial-of-service (ReDoS) attack. \n\n### Impact\n\nIf attacker can put a lot of JSX elements into `\u003cblockquote\u003e` tag, an internal regular expression for escaping characters may consume an excessive amount of computing resources.\n\n```javascript\n/** @jsxImportSource jsx-slack */\nimport { Section } from 'jsx-slack'\n\nconsole.log(\n  \u003cSection\u003e\n    \u003cblockquote\u003e\n      {[...Array(40)].map((_, i) =\u003e (\n        \u003cp\u003e{i + 1}\u003c/p\u003e\n      ))}\n    \u003c/blockquote\u003e\n  \u003c/Section\u003e\n)\n```\n\n### Patches\n\n_See also: https://github.com/yhatt/jsx-slack/security/advisories/GHSA-hp68-xhvj-x6j6_\n\njsx-slack v4.5.2 has updated regular expressions to prevent catastrophic backtracking.\n\njsx-slack v4.5.1 also had patched a workaround. It has no problems to contents with ASCII characters, but _still vulnerable to contents with multibyte characters_. (https://github.com/yhatt/jsx-slack/commit/36e4a10405e4c7745333e245fcc5029c02c7065d)\n\n### References\n\n- https://nvd.nist.gov/vuln/detail/CVE-2021-43838\n- https://github.com/yhatt/jsx-slack/commit/36e4a10405e4c7745333e245fcc5029c02c7065d\n\n### Credits\n\nThanks to @hieki for finding out this vulnerability.","status":"published","published":"2021-12-17T19:59:02Z","modified":"2023-07-21T19:15:59Z","cvss":[{"version":"3.1","score":3.7,"vector":"CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:N/I:N/A:L","level":"low"}],"cwes":["CWE-400","CWE-1333"],"updated_at":"2026-11-02T14:36:57.310051Z"}],"nvd":[{"id":"CVE-2021-43838","description":"jsx-slack is a library for building JSON objects for Slack Block Kit surfaces from JSX. In versions prior to 4.5.1 users are vulnerable to a regular expression denial-of-service (ReDoS) attack. If attacker can put a lot of JSX elements into `\u003cblockquote\u003e` tag, an internal regular expression for escaping characters may consume an excessive amount of computing resources. jsx-slack v4.5.1 has patched to a regex for escaping blockquote characters. Users are advised to upgrade as soon as possible.","status":"published","published":"2021-12-17T19:15:07.683Z","modified":"2026-06-17T04:11:32.663Z","cvss":[{"version":"3.1","score":5.3,"vector":"CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:L","level":"medium","assessor":"secondary"},{"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-400","CWE-1333"],"updated_at":"2026-11-02T14:07:02.566991Z"}],"osv":[{"id":"CVE-2021-43838","description":"jsx-slack is a library for building JSON objects for Slack Block Kit surfaces from JSX. In versions prior to 4.5.1 users are vulnerable to a regular expression denial-of-service (ReDoS) attack. If attacker can put a lot of JSX elements into `\u003cblockquote\u003e` tag, an internal regular expression for escaping characters may consume an excessive amount of computing resources. jsx-slack v4.5.1 has patched to a regex for escaping blockquote characters. Users are advised to upgrade as soon as possible.","status":"published","published":"2021-12-17T19:15:07.683Z","modified":"2026-10-20T10:55:04.957689952Z","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"}],"updated_at":"2026-11-02T15:44:21.877444Z"},{"id":"GHSA-55xv-f85c-248q","title":"Regular Expression Denial of Service (ReDoS) in jsx-slack","description":"jsx-slack v4.5.1 and earlier versions are vulnerable to a regular expression denial-of-service (ReDoS) attack. \n\n### Impact\n\nIf attacker can put a lot of JSX elements into `\u003cblockquote\u003e` tag, an internal regular expression for escaping characters may consume an excessive amount of computing resources.\n\n```javascript\n/** @jsxImportSource jsx-slack */\nimport { Section } from 'jsx-slack'\n\nconsole.log(\n  \u003cSection\u003e\n    \u003cblockquote\u003e\n      {[...Array(40)].map((_, i) =\u003e (\n        \u003cp\u003e{i + 1}\u003c/p\u003e\n      ))}\n    \u003c/blockquote\u003e\n  \u003c/Section\u003e\n)\n```\n\n### Patches\n\n_See also: https://github.com/yhatt/jsx-slack/security/advisories/GHSA-hp68-xhvj-x6j6_\n\njsx-slack v4.5.2 has updated regular expressions to prevent catastrophic backtracking.\n\njsx-slack v4.5.1 also had patched a workaround. It has no problems to contents with ASCII characters, but _still vulnerable to contents with multibyte characters_. (https://github.com/yhatt/jsx-slack/commit/36e4a10405e4c7745333e245fcc5029c02c7065d)\n\n### References\n\n- https://nvd.nist.gov/vuln/detail/CVE-2021-43838\n- https://github.com/yhatt/jsx-slack/commit/36e4a10405e4c7745333e245fcc5029c02c7065d\n\n### Credits\n\nThanks to @hieki for finding out this vulnerability.","status":"published","published":"2021-12-17T19:59:02Z","modified":"2026-07-08T06:26:54.469704888Z","cvss":[{"version":"3.1","score":3.7,"vector":"CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:N/I:N/A:L","level":"low"}],"cwes":["CWE-1333","CWE-400"],"updated_at":"2026-11-02T15:46:37.864461Z"}]}}