{"id":"CVE-2026-27469","aliases":["EUVD-2026-7721","GHSA-9fww-8cpr-q66r","PYSEC-2026-2527"],"status":"published","title":"Isso: Stored XSS via comment website field","description":"Isso is a lightweight commenting server written in Python and JavaScript. In commits before 0afbfe0691ee237963e8fb0b2ee01c9e55ca2144, there is a stored Cross-Site Scripting (XSS) vulnerability affecting the website and author comment fields. The website field was HTML-escaped using quote=False, which left single and double quotes unescaped. Since the frontend inserts the website value directly into a single-quoted href attribute via string concatenation, a single quote in the URL breaks out of the attribute context, allowing injection of arbitrary event handlers (e.g. onmouseover, onclick). The same escaping is missing entirely from the user-facing comment edit endpoint (PUT /id/) and the moderation edit endpoint (POST /id//edit/). This issue has been patched in commit 0afbfe0691ee237963e8fb0b2ee01c9e55ca2144. To workaround, nabling comment moderation (moderation = enabled = true in isso.cfg) prevents unauthenticated users from publishing comments, raising the bar for exploitation, but it does not fully mitigate the issue since a moderator activating a malicious comment would still expose visitors.","severity":{"version":"3.1","score":6.1,"vector":"CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:C/C:L/I:L/A:N","level":"medium","assessor":"cna","from":"cve"},"epss":{"day":"2026-11-12","score":0.00259,"percentile":0.17753,"model":"v2026.06.15"},"facts":{"in_kev":false,"known_exploited":false,"public_exploit":false,"fix_available":true},"cwes":["CWE-116","CWE-79"],"published":"2026-02-21T07:24:38Z","modified":"2026-10-28T02:30:23Z","fixes":[{"ecosystem":"PyPI","package":"isso","fixed_in":["0.13.2"],"sources":["ghsa","osv"]}],"affected":[{"source":"ghsa","ecosystem":"PyPI","package":"isso","ranges":[{"type":"ECOSYSTEM","events":[{"introduced":"0"},{"fixed":"0.13.2"}]}]},{"source":"osv","ecosystem":"PyPI","package":"isso","ranges":[{"type":"ECOSYSTEM","events":[{"introduced":"0"},{"fixed":"0.13.2"}]}],"versions":["0.10","0.10.1","0.10.2","0.10.3","0.10.4","0.10.5","0.10.6","0.11.0","0.11.1","0.12.0","0.12.1","0.12.2","0.12.4","0.12.5","0.12.6","0.12.6.1","0.12.6.2","0.13.0","0.13.1.dev0","0.8","0.8.1","0.8.2","0.8.3","0.9","0.9.1","0.9.10","0.9.2","0.9.3","0.9.4","0.9.5","0.9.6","0.9.7","0.9.8","0.9.9"]},{"source":"osv","ecosystem":"PyPI","package":"isso","ranges":[{"type":"ECOSYSTEM","events":[{"introduced":"0"},{"fixed":"0.13.2"}]}],"versions":["0.10","0.10.1","0.10.2","0.10.3","0.10.4","0.10.5","0.10.6","0.11.0","0.11.1","0.12.0","0.12.1","0.12.2","0.12.4","0.12.5","0.12.6","0.12.6.1","0.12.6.2","0.13.0","0.13.1.dev0","0.8","0.8.1","0.8.2","0.8.3","0.9","0.9.1","0.9.10","0.9.2","0.9.3","0.9.4","0.9.5","0.9.6","0.9.7","0.9.8","0.9.9"]}],"products":[{"vendor":"isso-comments","product":"isso"}],"references":[{"url":"https://github.com/isso-comments/isso/security/advisories/GHSA-9fww-8cpr-q66r","tags":["x_refsource_CONFIRM","advisory","web"]},{"url":"https://github.com/isso-comments/isso/commit/0afbfe0691ee237963e8fb0b2ee01c9e55ca2144","tags":["x_refsource_MISC","fix","web"]},{"url":"https://docs.python.org/3/library/html.html#html.escape","tags":["x_refsource_MISC","web"]},{"url":"https://nvd.nist.gov/vuln/detail/CVE-2026-27469","tags":["advisory"]},{"url":"https://github.com/advisories/GHSA-9fww-8cpr-q66r","tags":["advisory"]},{"url":"https://github.com/CVEProject/cvelistV5/tree/main/cves/2026/27xxx/CVE-2026-27469.json","tags":["advisory"]},{"url":"https://github.com/isso-comments/isso","tags":["package"]},{"url":"https://pypi.org/project/isso","tags":["package"]}],"sources":{"cve":[{"id":"CVE-2026-27469","title":"Isso: Stored XSS via comment website field","description":"Isso is a lightweight commenting server written in Python and JavaScript. In commits before 0afbfe0691ee237963e8fb0b2ee01c9e55ca2144, there is a stored Cross-Site Scripting (XSS) vulnerability affecting the website and author comment fields. The website field was HTML-escaped using quote=False, which left single and double quotes unescaped. Since the frontend inserts the website value directly into a single-quoted href attribute via string concatenation, a single quote in the URL breaks out of the attribute context, allowing injection of arbitrary event handlers (e.g. onmouseover, onclick). The same escaping is missing entirely from the user-facing comment edit endpoint (PUT /id/) and the moderation edit endpoint (POST /id//edit/). This issue has been patched in commit 0afbfe0691ee237963e8fb0b2ee01c9e55ca2144. To workaround, nabling comment moderation (moderation = enabled = true in isso.cfg) prevents unauthenticated users from publishing comments, raising the bar for exploitation, but it does not fully mitigate the issue since a moderator activating a malicious comment would still expose visitors.","status":"published","published":"2026-02-21T07:24:38.971Z","modified":"2026-02-24T18:50:07.65Z","cvss":[{"version":"3.1","score":6.1,"vector":"CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:C/C:L/I:L/A:N","level":"medium","assessor":"cna"}],"cwes":["CWE-79","CWE-116"],"updated_at":"2026-11-02T14:19:48.826324Z"}],"euvd":[{"id":"EUVD-2026-7721","description":"Isso is a lightweight commenting server written in Python and JavaScript. In commits before 0afbfe0691ee237963e8fb0b2ee01c9e55ca2144, there is a stored Cross-Site Scripting (XSS) vulnerability affecting the website and author comment fields. The website field was HTML-escaped using quote=False, which left single and double quotes unescaped. Since the frontend inserts the website value directly into a single-quoted href attribute via string concatenation, a single quote in the URL breaks out of the attribute context, allowing injection of arbitrary event handlers (e.g. onmouseover, onclick). The same escaping is missing entirely from the user-facing comment edit endpoint (PUT /id/) and the moderation edit endpoint (POST /id//edit/). This issue has been patched in commit 0afbfe0691ee237963e8fb0b2ee01c9e55ca2144. To workaround, nabling comment moderation (moderation = enabled = true in isso.cfg) prevents unauthenticated users from publishing comments, raising the bar for exploitation, but it does not fully mitigate the issue since a moderator activating a malicious comment would still expose visitors.","status":"published","published":"2026-02-21T07:24:38Z","modified":"2026-02-24T18:50:07Z","cvss":[{"version":"3.1","score":6.1,"vector":"CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:C/C:L/I:L/A:N","level":"medium"}],"updated_at":"2026-11-02T19:48:29.958768Z"}],"ghsa":[{"id":"GHSA-9fww-8cpr-q66r","title":"Isso affected by Stored XSS via comment website field","description":"## Impact\n\nThis is a stored Cross-Site Scripting (XSS) vulnerability affecting the website and author comment fields. The website field was HTML-escaped using quote=False, which left single and double quotes unescaped. Since the frontend inserts the website value directly into a single-quoted href attribute via string concatenation, a single quote in the URL breaks out of the attribute context, allowing injection of arbitrary event handlers (e.g. onmouseover, onclick).\n\nThe same escaping was missing entirely from the user-facing comment edit endpoint (PUT /id/\u003cid\u003e) and the moderation edit endpoint (POST /id/\u003cid\u003e/edit/\u003ckey\u003e).\n\nAny visitor to a page embedding isso comments is impacted. No authentication or interaction beyond mouse movement is required to trigger a payload — an attacker can post a comment anonymously (moderation is off by default) with a crafted website URL, and the payload persists in the database and fires on every page load. With the full-page invisible overlay technique described in the report, the victim only needs to move their mouse.\n\n## Patches\n\nThe issue is fixed in commit 3cf27c2. Users should upgrade to a version containing that commit once released. The fix applies html.escape(..., quote=True) to the website field across all three write paths (POST /new, PUT /id/\u003cid\u003e, POST /id/\u003cid\u003e/edit/\u003ckey\u003e), and adds input validation and escaping to the moderation edit endpoint which previously had neither.\n\n## Workarounds\n\n  Enabling comment moderation (moderation = enabled = true in isso.cfg) prevents unauthenticated users from publishing comments, raising the bar for exploitation. However, it\n  does not fully mitigate the issue since a moderator activating a malicious comment would still expose visitors. There is no configuration-only workaround that fully prevents\n   the vulnerability.\n\n## Resources\n\n  - https://docs.python.org/3/library/html.html#html.escape — note the quote parameter","status":"published","published":"2026-02-24T16:03:04Z","modified":"2026-02-24T16:03:04Z","cvss":[{"version":"3.1","score":6.1,"vector":"CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:C/C:L/I:L/A:N","level":"medium"}],"cwes":["CWE-79","CWE-116"],"updated_at":"2026-11-02T14:39:27.949248Z"}],"nvd":[{"id":"CVE-2026-27469","description":"Isso is a lightweight commenting server written in Python and JavaScript. In commits before 0afbfe0691ee237963e8fb0b2ee01c9e55ca2144, there is a stored Cross-Site Scripting (XSS) vulnerability affecting the website and author comment fields. The website field was HTML-escaped using quote=False, which left single and double quotes unescaped. Since the frontend inserts the website value directly into a single-quoted href attribute via string concatenation, a single quote in the URL breaks out of the attribute context, allowing injection of arbitrary event handlers (e.g. onmouseover, onclick). The same escaping is missing entirely from the user-facing comment edit endpoint (PUT /id/) and the moderation edit endpoint (POST /id//edit/). This issue has been patched in commit 0afbfe0691ee237963e8fb0b2ee01c9e55ca2144. To workaround, nabling comment moderation (moderation = enabled = true in isso.cfg) prevents unauthenticated users from publishing comments, raising the bar for exploitation, but it does not fully mitigate the issue since a moderator activating a malicious comment would still expose visitors.","status":"published","published":"2026-02-21T08:16:11.993Z","modified":"2026-06-17T10:27:12.31Z","cvss":[{"version":"3.1","score":6.1,"vector":"CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:C/C:L/I:L/A:N","level":"medium","assessor":"secondary"}],"cwes":["CWE-79","CWE-116"],"updated_at":"2026-11-02T14:12:06.63895Z"}],"osv":[{"id":"CVE-2026-27469","title":"Isso: Stored XSS via comment website field","description":"Isso is a lightweight commenting server written in Python and JavaScript. In commits before 0afbfe0691ee237963e8fb0b2ee01c9e55ca2144, there is a stored Cross-Site Scripting (XSS) vulnerability affecting the website and author comment fields. The website field was HTML-escaped using quote=False, which left single and double quotes unescaped. Since the frontend inserts the website value directly into a single-quoted href attribute via string concatenation, a single quote in the URL breaks out of the attribute context, allowing injection of arbitrary event handlers (e.g. onmouseover, onclick). The same escaping is missing entirely from the user-facing comment edit endpoint (PUT /id/) and the moderation edit endpoint (POST /id//edit/). This issue has been patched in commit 0afbfe0691ee237963e8fb0b2ee01c9e55ca2144. To workaround, nabling comment moderation (moderation = enabled = true in isso.cfg) prevents unauthenticated users from publishing comments, raising the bar for exploitation, but it does not fully mitigate the issue since a moderator activating a malicious comment would still expose visitors.","status":"published","published":"2026-02-21T07:24:38.971Z","modified":"2026-10-28T02:30:23.825311613Z","cvss":[{"version":"3.1","score":6.1,"vector":"CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:C/C:L/I:L/A:N","level":"medium"}],"cwes":["CWE-116","CWE-79"],"updated_at":"2026-11-02T15:45:00.180685Z"},{"id":"GHSA-9fww-8cpr-q66r","title":"Isso affected by Stored XSS via comment website field","description":"## Impact\n\nThis is a stored Cross-Site Scripting (XSS) vulnerability affecting the website and author comment fields. The website field was HTML-escaped using quote=False, which left single and double quotes unescaped. Since the frontend inserts the website value directly into a single-quoted href attribute via string concatenation, a single quote in the URL breaks out of the attribute context, allowing injection of arbitrary event handlers (e.g. onmouseover, onclick).\n\nThe same escaping was missing entirely from the user-facing comment edit endpoint (PUT /id/\u003cid\u003e) and the moderation edit endpoint (POST /id/\u003cid\u003e/edit/\u003ckey\u003e).\n\nAny visitor to a page embedding isso comments is impacted. No authentication or interaction beyond mouse movement is required to trigger a payload — an attacker can post a comment anonymously (moderation is off by default) with a crafted website URL, and the payload persists in the database and fires on every page load. With the full-page invisible overlay technique described in the report, the victim only needs to move their mouse.\n\n## Patches\n\nThe issue is fixed in commit 3cf27c2. Users should upgrade to a version containing that commit once released. The fix applies html.escape(..., quote=True) to the website field across all three write paths (POST /new, PUT /id/\u003cid\u003e, POST /id/\u003cid\u003e/edit/\u003ckey\u003e), and adds input validation and escaping to the moderation edit endpoint which previously had neither.\n\n## Workarounds\n\n  Enabling comment moderation (moderation = enabled = true in isso.cfg) prevents unauthenticated users from publishing comments, raising the bar for exploitation. However, it\n  does not fully mitigate the issue since a moderator activating a malicious comment would still expose visitors. There is no configuration-only workaround that fully prevents\n   the vulnerability.\n\n## Resources\n\n  - https://docs.python.org/3/library/html.html#html.escape — note the quote parameter","status":"published","published":"2026-02-24T16:03:04Z","modified":"2026-07-13T16:42:33.405962889Z","cvss":[{"version":"3.1","score":6.1,"vector":"CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:C/C:L/I:L/A:N","level":"medium"}],"cwes":["CWE-116","CWE-79"],"updated_at":"2026-11-02T15:46:43.875515Z"},{"id":"PYSEC-2026-2527","title":"Isso affected by Stored XSS via comment website field","description":"## Impact\n\nThis is a stored Cross-Site Scripting (XSS) vulnerability affecting the website and author comment fields. The website field was HTML-escaped using quote=False, which left single and double quotes unescaped. Since the frontend inserts the website value directly into a single-quoted href attribute via string concatenation, a single quote in the URL breaks out of the attribute context, allowing injection of arbitrary event handlers (e.g. onmouseover, onclick).\n\nThe same escaping was missing entirely from the user-facing comment edit endpoint (PUT /id/\u003cid\u003e) and the moderation edit endpoint (POST /id/\u003cid\u003e/edit/\u003ckey\u003e).\n\nAny visitor to a page embedding isso comments is impacted. No authentication or interaction beyond mouse movement is required to trigger a payload — an attacker can post a comment anonymously (moderation is off by default) with a crafted website URL, and the payload persists in the database and fires on every page load. With the full-page invisible overlay technique described in the report, the victim only needs to move their mouse.\n\n## Patches\n\nThe issue is fixed in commit 3cf27c2. Users should upgrade to a version containing that commit once released. The fix applies html.escape(..., quote=True) to the website field across all three write paths (POST /new, PUT /id/\u003cid\u003e, POST /id/\u003cid\u003e/edit/\u003ckey\u003e), and adds input validation and escaping to the moderation edit endpoint which previously had neither.\n\n## Workarounds\n\n  Enabling comment moderation (moderation = enabled = true in isso.cfg) prevents unauthenticated users from publishing comments, raising the bar for exploitation. However, it\n  does not fully mitigate the issue since a moderator activating a malicious comment would still expose visitors. There is no configuration-only workaround that fully prevents\n   the vulnerability.\n\n## Resources\n\n  - https://docs.python.org/3/library/html.html#html.escape — note the quote parameter","status":"published","published":"2026-07-13T14:36:38.311279Z","modified":"2026-07-13T16:31:58.129063476Z","cvss":[{"version":"3.1","score":6.1,"vector":"CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:C/C:L/I:L/A:N","level":"medium"}],"updated_at":"2026-11-02T15:52:55.961245Z"}]}}