CVE-2026-30913: Flarum/nicknames Flarum/nicknames Extension Has Display Name Vulnerability

{
  "schema_version" : "1.4.0",
  "id" : "GHSA-3c4m-j3g4-hh25",
  "modified" : "2026-03-10T18:44:19Z",
  "published" : "2026-03-10T00:56:30Z",
  "aliases" : [ "CVE-2026-30913" ],
  "summary" : "flarum/nicknames extension has display name injection in notification emails (autolink & markdown)",
  "details" : "## Summary\n\nWhen the `flarum/nicknames` extension is enabled, a registered user can set their nickname to a string that email clients interpret as a hyperlink. The nickname is inserted verbatim into plain-text notification emails, and recipients may be misled into visiting attacker-controlled domains.\n\n## Affected package\n\n- **`flarum/nicknames`** — permissive display name driver that allows special characters; affected since initial release on the `1.x` branch\n\nAny third-party display name driver that permits special characters would be equally affected.\n\n## Variants\n\n1. **Domain autolink** — a nickname such as `nasty.com` is automatically converted to a clickable hyperlink by virtually all email clients (Gmail, Outlook, Apple Mail, Thunderbird).\n2. **Markdown link syntax** — a nickname such as `[CLICK](https://evil.com)` is rendered as a clickable hyperlink by email clients that auto-render markdown in plain-text emails (e.g. Apple Mail, Thunderbird).\n\n## Steps to reproduce\n\n**Variant 1 (autolink — affects all email clients)**\n1. Enable `flarum/nicknames`, set nickname to `nasty.com`\n2. Trigger a notification email to another user (e.g. follow them, mention them)\n3. The nickname appears as a clickable link in the received email\n\n**Variant 2 (markdown — affects markdown-rendering email clients)**\n1. Enable `flarum/nicknames`, set nickname to `[CLICK](https://evil.com)`\n2. Trigger a notification email to another user\n3. In a markdown-rendering email client (e.g. Apple Mail), the nickname appears as a clickable link\n\n## Impact\n\nPhishing / social engineering: victims may be misled into visiting attacker-controlled URLs via links appearing to originate from a trusted platform notification email. Variant 1 is exploitable against virtually all email clients without any special conditions.\n\n- CVSS v3.1: `AV:N/AC:L/PR:L/UI:R/S:U/C:L/I:L/A:N` — **4.6 Medium**\n\n## Root cause\n\nThe default username-based display name driver constrains values to `[a-zA-Z0-9_-]+`, making it immune. `flarum/nicknames` introduced permissive validation (min/max length and an optional admin-configured regex) that allows arbitrary characters including those meaningful in URL and markdown contexts. This has been the case since the first commit of the extension.\n\n## Proposed fix\n\n- Add validation in `flarum/nicknames` to reject or sanitize nicknames containing characters that email clients may interpret as URLs or markdown links\n- Alternatively, sanitize the display name before insertion into notification email bodies so that legitimate nicknames like `Jane.Smith` are preserved but rendered safely\n\n## References\n\n- Bug bounty submission: SBB-L4ZVAFH8 (Intigriti)",
  "severity" : [ {
    "type" : "CVSS_V3",
    "score" : "CVSS:3.1/AV:N/AC:L/PR:L/UI:R/S:U/C:L/I:L/A:N"
  } ],
  "affected" : [ {
    "package" : {
      "ecosystem" : "Packagist",
      "name" : "flarum/nicknames"
    },
    "ranges" : [ {
      "type" : "ECOSYSTEM",
      "events" : [ {
        "introduced" : "0"
      }, {
        "fixed" : "1.8.3"
      } ]
    } ]
  } ],
  "references" : [ {
    "type" : "WEB",
    "url" : "https://github.com/flarum/framework/security/advisories/GHSA-3c4m-j3g4-hh25"
  }, {
    "type" : "ADVISORY",
    "url" : "https://nvd.nist.gov/vuln/detail/CVE-2026-30913"
  }, {
    "type" : "WEB",
    "url" : "https://github.com/flarum/nicknames/commit/4dde99729abdce8f6e2a7437c86e38735fdcca28"
  }, {
    "type" : "PACKAGE",
    "url" : "https://github.com/flarum/framework"
  }, {
    "type" : "WEB",
    "url" : "https://github.com/flarum/nicknames/releases/tag/v1.8."
  }, {
    "type" : "WEB",
    "url" : "https://github.com/flarum/nicknames/releases/tag/v1.8.3"
  } ],
  "database_specific" : {
    "cwe_ids" : [ "CWE-79" ],
    "severity" : "MODERATE",
    "github_reviewed" : true,
    "github_reviewed_at" : "2026-03-10T00:56:30Z",
    "nvd_published_at" : "2026-03-10T17:40:15Z"
  }
}