{
  "cveId": "CVE-2021-29991",
  "url": "https://patchblox.com/security/cve/CVE-2021-29991",
  "summary": "CVE-2021-29991 is fixed in 11 products on 2 platforms, first by firefox 91.0.1\u002Bbuild1-0ubuntu0.18.04.1, released August 17, 2021. It is not reported as exploited. Patch Radar priority: High.",
  "title": "Firefox ESR and 3 others: Firefox incorrectly accepted a newline in a HTTP/3 header, interpretting it as two separate headers.",
  "description": "Firefox incorrectly accepted a newline in a HTTP/3 header, interpretting it as two separate headers. This allowed for a header splitting attack against servers using HTTP/3. This vulnerability affects Firefox \u003C 91.0.1 and Thunderbird \u003C 91.0.1.",
  "published": "2021-08-17T17:00:00Z",
  "severity": "Medium",
  "cvss": 8.1,
  "epss": 0.0091,
  "epssPercentile": 0.60216,
  "priority": "High",
  "priorityTier": 3,
  "exploited": false,
  "vendorExploited": false,
  "disclosed": false,
  "vendorAdvisory": "https://nvd.nist.gov/vuln/detail/CVE-2021-29991",
  "fixes": [
    {
      "platform": "windows-app",
      "product": "Mozilla Firefox ESR (en-US)",
      "fixedVersion": "91.3.0",
      "fix": "Mozilla Firefox ESR (en-US) 91.3.0",
      "url": "https://patchblox.com/security/fix/windows-app/mozilla.firefox.esr-91.3.0",
      "released": "2021-10-28T00:00:00Z"
    },
    {
      "platform": "windows-app",
      "product": "Mozilla Thunderbird (en-US)",
      "fixedVersion": "91.0.3",
      "fix": "Mozilla Thunderbird (en-US) 91.0.3",
      "url": "https://patchblox.com/security/fix/windows-app/mozilla.thunderbird-91.0.3",
      "released": "2021-08-24T00:00:00Z"
    },
    {
      "platform": "linux",
      "product": "firefox",
      "release": "Ubuntu 18.04.6 LTS (bionic)",
      "fixedVersion": "91.0.1\u002Bbuild1-0ubuntu0.18.04.1",
      "fix": "firefox 91.0.1\u002Bbuild1-0ubuntu0.18.04.1",
      "url": "https://patchblox.com/security/fix/linux/ubuntu-bionic-firefox-91.0.1-build1-0ubuntu0.18.04.1",
      "released": "2021-08-17T17:00:00Z"
    },
    {
      "platform": "linux",
      "product": "firefox",
      "release": "Ubuntu 20.04 LTS (focal)",
      "fixedVersion": "91.0.1\u002Bbuild1-0ubuntu0.20.04.1",
      "fix": "firefox 91.0.1\u002Bbuild1-0ubuntu0.20.04.1",
      "url": "https://patchblox.com/security/fix/linux/ubuntu-focal-firefox-91.0.1-build1-0ubuntu0.20.04.1",
      "released": "2021-08-17T17:00:00Z"
    },
    {
      "platform": "linux",
      "product": "firefox-geckodriver",
      "release": "Ubuntu 18.04.6 LTS (bionic)",
      "fixedVersion": "91.0.1\u002Bbuild1-0ubuntu0.18.04.1",
      "fix": "firefox-geckodriver 91.0.1\u002Bbuild1-0ubuntu0.18.04.1",
      "url": "https://patchblox.com/security/fix/linux/ubuntu-bionic-firefox-geckodriver-91.0.1-build1-0ubuntu0.18.04.1",
      "released": "2021-08-17T17:00:00Z"
    },
    {
      "platform": "linux",
      "product": "firefox-geckodriver",
      "release": "Ubuntu 20.04 LTS (focal)",
      "fixedVersion": "91.0.1\u002Bbuild1-0ubuntu0.20.04.1",
      "fix": "firefox-geckodriver 91.0.1\u002Bbuild1-0ubuntu0.20.04.1",
      "url": "https://patchblox.com/security/fix/linux/ubuntu-focal-firefox-geckodriver-91.0.1-build1-0ubuntu0.20.04.1",
      "released": "2021-08-17T17:00:00Z"
    },
    {
      "platform": "linux",
      "product": "firefox-mozsymbols",
      "release": "Ubuntu 18.04.6 LTS (bionic)",
      "fixedVersion": "91.0.1\u002Bbuild1-0ubuntu0.18.04.1",
      "fix": "firefox-mozsymbols 91.0.1\u002Bbuild1-0ubuntu0.18.04.1",
      "url": "https://patchblox.com/security/fix/linux/ubuntu-bionic-firefox-mozsymbols-91.0.1-build1-0ubuntu0.18.04.1",
      "released": "2021-08-17T17:00:00Z"
    },
    {
      "platform": "linux",
      "product": "firefox-mozsymbols",
      "release": "Ubuntu 20.04 LTS (focal)",
      "fixedVersion": "91.0.1\u002Bbuild1-0ubuntu0.20.04.1",
      "fix": "firefox-mozsymbols 91.0.1\u002Bbuild1-0ubuntu0.20.04.1",
      "url": "https://patchblox.com/security/fix/linux/ubuntu-focal-firefox-mozsymbols-91.0.1-build1-0ubuntu0.20.04.1",
      "released": "2021-08-17T17:00:00Z"
    },
    {
      "platform": "linux",
      "product": "thunderbird",
      "release": "Ubuntu 18.04.6 LTS (bionic)",
      "fixedVersion": "1:91.5.0\u002Bbuild1-0ubuntu0.18.04.1",
      "fix": "thunderbird 1:91.5.0\u002Bbuild1-0ubuntu0.18.04.1",
      "url": "https://patchblox.com/security/fix/linux/ubuntu-bionic-thunderbird-1-91.5.0-build1-0ubuntu0.18.04.1",
      "released": "2023-02-16T14:15:00Z"
    },
    {
      "platform": "linux",
      "product": "thunderbird",
      "release": "Ubuntu 20.04 LTS (focal)",
      "fixedVersion": "1:91.5.0\u002Bbuild1-0ubuntu0.20.04.1",
      "fix": "thunderbird 1:91.5.0\u002Bbuild1-0ubuntu0.20.04.1",
      "url": "https://patchblox.com/security/fix/linux/ubuntu-focal-thunderbird-1-91.5.0-build1-0ubuntu0.20.04.1",
      "released": "2023-02-16T14:15:00Z"
    },
    {
      "platform": "linux",
      "product": "thunderbird-gnome-support",
      "release": "Ubuntu 18.04.6 LTS (bionic)",
      "fixedVersion": "1:91.5.0\u002Bbuild1-0ubuntu0.18.04.1",
      "fix": "thunderbird-gnome-support 1:91.5.0\u002Bbuild1-0ubuntu0.18.04.1",
      "url": "https://patchblox.com/security/fix/linux/ubuntu-bionic-thunderbird-gnome-support-1-91.5.0-build1-0ubuntu0.18.04.1",
      "released": "2023-02-16T14:15:00Z"
    },
    {
      "platform": "linux",
      "product": "thunderbird-gnome-support",
      "release": "Ubuntu 20.04 LTS (focal)",
      "fixedVersion": "1:91.5.0\u002Bbuild1-0ubuntu0.20.04.1",
      "fix": "thunderbird-gnome-support 1:91.5.0\u002Bbuild1-0ubuntu0.20.04.1",
      "url": "https://patchblox.com/security/fix/linux/ubuntu-focal-thunderbird-gnome-support-1-91.5.0-build1-0ubuntu0.20.04.1",
      "released": "2023-02-16T14:15:00Z"
    },
    {
      "platform": "linux",
      "product": "thunderbird-mozsymbols",
      "release": "Ubuntu 18.04.6 LTS (bionic)",
      "fixedVersion": "1:91.5.0\u002Bbuild1-0ubuntu0.18.04.1",
      "fix": "thunderbird-mozsymbols 1:91.5.0\u002Bbuild1-0ubuntu0.18.04.1",
      "url": "https://patchblox.com/security/fix/linux/ubuntu-bionic-thunderbird-mozsymbols-1-91.5.0-build1-0ubuntu0.18.04.1",
      "released": "2023-02-16T14:15:00Z"
    },
    {
      "platform": "linux",
      "product": "thunderbird-mozsymbols",
      "release": "Ubuntu 20.04 LTS (focal)",
      "fixedVersion": "1:91.5.0\u002Bbuild1-0ubuntu0.20.04.1",
      "fix": "thunderbird-mozsymbols 1:91.5.0\u002Bbuild1-0ubuntu0.20.04.1",
      "url": "https://patchblox.com/security/fix/linux/ubuntu-focal-thunderbird-mozsymbols-1-91.5.0-build1-0ubuntu0.20.04.1",
      "released": "2023-02-16T14:15:00Z"
    },
    {
      "platform": "linux",
      "product": "xul-ext-calendar-timezones",
      "release": "Ubuntu 18.04.6 LTS (bionic)",
      "fixedVersion": "1:91.5.0\u002Bbuild1-0ubuntu0.18.04.1",
      "fix": "xul-ext-calendar-timezones 1:91.5.0\u002Bbuild1-0ubuntu0.18.04.1",
      "url": "https://patchblox.com/security/fix/linux/ubuntu-bionic-xul-ext-calendar-timezones-1-91.5.0-build1-0ubuntu0.18.04.1",
      "released": "2023-02-16T14:15:00Z"
    },
    {
      "platform": "linux",
      "product": "xul-ext-calendar-timezones",
      "release": "Ubuntu 20.04 LTS (focal)",
      "fixedVersion": "1:91.5.0\u002Bbuild1-0ubuntu0.20.04.1",
      "fix": "xul-ext-calendar-timezones 1:91.5.0\u002Bbuild1-0ubuntu0.20.04.1",
      "url": "https://patchblox.com/security/fix/linux/ubuntu-focal-xul-ext-calendar-timezones-1-91.5.0-build1-0ubuntu0.20.04.1",
      "released": "2023-02-16T14:15:00Z"
    },
    {
      "platform": "linux",
      "product": "xul-ext-gdata-provider",
      "release": "Ubuntu 18.04.6 LTS (bionic)",
      "fixedVersion": "1:91.5.0\u002Bbuild1-0ubuntu0.18.04.1",
      "fix": "xul-ext-gdata-provider 1:91.5.0\u002Bbuild1-0ubuntu0.18.04.1",
      "url": "https://patchblox.com/security/fix/linux/ubuntu-bionic-xul-ext-gdata-provider-1-91.5.0-build1-0ubuntu0.18.04.1",
      "released": "2023-02-16T14:15:00Z"
    },
    {
      "platform": "linux",
      "product": "xul-ext-gdata-provider",
      "release": "Ubuntu 20.04 LTS (focal)",
      "fixedVersion": "1:91.5.0\u002Bbuild1-0ubuntu0.20.04.1",
      "fix": "xul-ext-gdata-provider 1:91.5.0\u002Bbuild1-0ubuntu0.20.04.1",
      "url": "https://patchblox.com/security/fix/linux/ubuntu-focal-xul-ext-gdata-provider-1-91.5.0-build1-0ubuntu0.20.04.1",
      "released": "2023-02-16T14:15:00Z"
    },
    {
      "platform": "linux",
      "product": "xul-ext-lightning",
      "release": "Ubuntu 18.04.6 LTS (bionic)",
      "fixedVersion": "1:91.5.0\u002Bbuild1-0ubuntu0.18.04.1",
      "fix": "xul-ext-lightning 1:91.5.0\u002Bbuild1-0ubuntu0.18.04.1",
      "url": "https://patchblox.com/security/fix/linux/ubuntu-bionic-xul-ext-lightning-1-91.5.0-build1-0ubuntu0.18.04.1",
      "released": "2023-02-16T14:15:00Z"
    },
    {
      "platform": "linux",
      "product": "xul-ext-lightning",
      "release": "Ubuntu 20.04 LTS (focal)",
      "fixedVersion": "1:91.5.0\u002Bbuild1-0ubuntu0.20.04.1",
      "fix": "xul-ext-lightning 1:91.5.0\u002Bbuild1-0ubuntu0.20.04.1",
      "url": "https://patchblox.com/security/fix/linux/ubuntu-focal-xul-ext-lightning-1-91.5.0-build1-0ubuntu0.20.04.1",
      "released": "2023-02-16T14:15:00Z"
    }
  ],
  "noFixYet": [],
  "dataAsOf": "2026-11-09T13:31:49Z",
  "attribution": {
    "text": "Data: Patchblox Patch Radar",
    "url": "https://patchblox.com/security/patch-radar",
    "terms": "https://patchblox.com/security/patch-radar/use-the-data"
  }
}