{
  "affected": [
    {
      "ranges": [
        {
          "database_specific": {
            "cpe": "cpe:2.3:a:mattermost:mattermost_server:*:*:*:*:*:*:*:*",
            "extracted_events": [
              {
                "introduced": "11.4.0"
              },
              {
                "fixed": "11.4.4"
              },
              {
                "introduced": "11.5.0"
              },
              {
                "fixed": "11.5.2"
              }
            ],
            "source": "CPE_RANGE"
          },
          "events": [
            {
              "introduced": "2a1ac98bd3fae587927adf9340ba266c8c02018e"
            },
            {
              "fixed": "37b08cfe7154241c2c6a8af0fd500e0785bbc900"
            },
            {
              "introduced": "9f2616376582893035a7e3cb38b0fab648bba4e8"
            },
            {
              "fixed": "cc4ef6863ee114bc96be4e34478ec2f0db3eac4e"
            }
          ],
          "repo": "https://github.com/mattermost/mattermost",
          "type": "GIT"
        }
      ]
    }
  ],
  "database_specific": {
    "cna_assigner": "Mattermost",
    "cwe_ids": [
      "CWE-346"
    ],
    "osv_generated_from": "https://github.com/CVEProject/cvelistV5/tree/main/cves/2026/6xxx/CVE-2026-6339.json",
    "unresolved_ranges": [
      {
        "extracted_events": [
          {
            "introduced": "11.5.0"
          },
          {
            "last_affected": "11.5.1"
          },
          {
            "introduced": "11.4.0"
          },
          {
            "last_affected": "11.4.3"
          }
        ],
        "source": "AFFECTED_FIELD"
      }
    ]
  },
  "details": "Mattermost versions 11.5.x \u003c= 11.5.1, 11.4.x \u003c= 11.4.3 fail to validate the X-Requested-With header on the burn-on-read reveal endpoint which allows an authenticated channel member to force the reveal of a burn-on-read message without recipient consent via a crafted Markdown image tag.. Mattermost Advisory ID: MMSA-2026-00636",
  "id": "CVE-2026-6339",
  "modified": "2026-07-08T05:39:16.431230684Z",
  "published": "2026-05-18T08:05:30.925Z",
  "references": [
    {
      "type": "ADVISORY",
      "url": "https://github.com/CVEProject/cvelistV5/tree/main/cves/2026/6xxx/CVE-2026-6339.json"
    },
    {
      "type": "ADVISORY",
      "url": "https://mattermost.com/security-updates"
    },
    {
      "type": "ADVISORY",
      "url": "https://nvd.nist.gov/vuln/detail/CVE-2026-6339"
    }
  ],
  "schema_version": "1.7.5",
  "severity": [
    {
      "score": "CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:L",
      "type": "CVSS_V3"
    }
  ],
  "summary": "Missing request origin validation on burn-on-read reveal endpoint"
}