{"answers":{"affected":"14 open source packages ship an affected version, including github.com/mattermost/mattermost-server, github.com/mattermost/mattermost-server/v5 and github.com/mattermost/mattermost-server/v6. It affects 1 product.","exploited":"There is no known exploitation of CVE-2026-5740 in the wild and no public exploit code.","fix":"Upgrade github.com/mattermost/mattermost-server to a fixed version for your release line: 10.11.15, 10.11.15+incompatible, 11.4.5+incompatible or 11.5.4+incompatible.","what":"CVE-2026-5740 is a high-severity denial of service vulnerability in Mattermost Mattermost Server, published on 22 May 2026. An attacker can exploit it over the internet without logging in, with no action from the victim."},"fix_prompt":"Check this codebase for CVE-2026-5740 and fix it if it is affected.\n\nWhat it is: CVE-2026-5740 is a high-severity denial of service vulnerability in Mattermost Mattermost Server, published on 22 May 2026. An attacker can exploit it over the internet without logging in, with no action from the victim.\nExploitation: There is no known exploitation of CVE-2026-5740 in the wild and no public exploit code.\n\nAffected packages and fixed versions:\n- github.com/mattermost/mattermost-server (Go): affected from 10.11.0; fixed in 10.11.15\n- github.com/mattermost/mattermost-server (Go): affected from 10.11.0; fixed in 10.11.15\n- github.com/mattermost/mattermost-server (Go): affected from 10.11.0+incompatible; fixed in 10.11.15+incompatible, 11.4.5+incompatible, 11.5.4+incompatible, 11.6.1+incompatible\n- github.com/mattermost/mattermost-server (Go): affected from 11.4.0; fixed in 11.4.5\n- github.com/mattermost/mattermost-server (Go): affected from 11.4.0; fixed in 11.4.5\n- github.com/mattermost/mattermost-server (Go): affected from 11.5.0; fixed in 11.5.4\n- github.com/mattermost/mattermost-server (Go): affected from 11.5.0; fixed in 11.5.4\n- github.com/mattermost/mattermost-server (Go): affected from 11.6.0; fixed in 11.6.1\n- github.com/mattermost/mattermost-server (Go): affected from 11.6.0; fixed in 11.6.1\n- github.com/mattermost/mattermost-server/v5 (Go): affected all versions; no fix listed\n- github.com/mattermost/mattermost-server/v6 (Go): affected all versions; no fix listed\n- github.com/mattermost/mattermost/server/v8 (Go): affected all versions; fixed in 8.0.0-20260410202636-17939826efa2\n\nTask:\n1. Search the dependency manifests and lockfiles (for example package.json, package-lock.json, requirements.txt, poetry.lock, uv.lock, pom.xml, build.gradle, go.mod, Cargo.lock, Gemfile.lock) and any Dockerfiles for the affected packages, including transitive dependencies.\n2. If an affected version is in use, upgrade it to the fixed version for its release line with the project's package manager, so the lockfile is regenerated. Prefer the smallest upgrade that fixes it.\n3. If there is no fix, or the upgrade would break the build, do not guess: explain the risk and the safest workaround instead.\n4. Run the tests and summarise what changed and why.\n5. If nothing in the project is affected, say so and change nothing.\n\nReference: https://insights.sbomify.com/CVE-2026-5740/ (Markdown: https://insights.sbomify.com/CVE-2026-5740/index.md)","id":"CVE-2026-5740","markdown":"https://insights.sbomify.com/CVE-2026-5740/index.md","name":"CVE-2026-5740","record":{"aliases":["GHSA-w9m8-p4cc-4qj9","GO-2026-5838"],"analysis":{"component_type":"server_software","fix_type":"upgrade","impacts":["denial_of_service"],"network_reachable":"yes","non_default_config":false,"product_category":"Mattermost Server","requires_auth":"none","summary":"Unauthenticated attackers can crash the Mattermost server by sending crafted WebSocket messages, causing a full service outage.","user_interaction":"not_required","vuln_class":"denial_of_service"},"analysis_generated_by":"qwen3.8-flash-next","assigner":"Mattermost","cpe":[{"product":"mattermost_server","vendor":"mattermost"}],"cvss":{"score":7.5,"severity":"high","source":"cna","vector":"CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H","version":"3.1"},"cwes":[{"id":"CWE-789","name":"Memory Allocation with Excessive Size Value"}],"description":"Mattermost versions 11.6.x \u003c= 11.6.0, 11.5.x \u003c= 11.5.3, 11.4.x \u003c= 11.4.4, 10.11.x \u003c= 10.11.14 fail to properly validate msgpack-encoded WebSocket frames before memory allocation which allows an unauthenticated remote attacker to crash the server process and cause a full service outage for all users via a crafted binary WebSocket message sent to the public WebSocket endpoint.. Mattermost Advisory ID: MMSA-2026-00647","ecosystems":["Go"],"exploits":{"exploitdb":0,"first_seen":null,"github_poc":0,"max_poc_stars":null,"metasploit":0,"nuclei":0,"refs":[],"tier":"none_known"},"has_fix":true,"headline":"Unauthenticated WebSocket binary frame causes denial of service in Mattermost Server","id":"CVE-2026-5740","indexable":true,"kev":null,"kind":"cve","links":{"ecosystem":"Go","product":"mattermost:mattermost_server","products":["mattermost:mattermost_server"],"type":"denial_of_service","year":"2026"},"n_packages":14,"n_references":1,"next":{"headline":"suvarchal docker-mcp-server HTTP index.ts pull_image os command injection","id":"CVE-2026-5741"},"packages":[{"ecosystem":"Go","fixed":["10.11.15"],"introduced":["10.11.0"],"last_affected":[],"package":"github.com/mattermost/mattermost-server","purl":null,"source":"GHSA-w9m8-p4cc-4qj9"},{"ecosystem":"Go","fixed":["10.11.15"],"introduced":["10.11.0"],"last_affected":[],"package":"github.com/mattermost/mattermost-server","purl":"pkg:golang/github.com/mattermost/mattermost-server","source":"GHSA-w9m8-p4cc-4qj9"},{"ecosystem":"Go","fixed":["10.11.15+incompatible","11.4.5+incompatible","11.5.4+incompatible","11.6.1+incompatible"],"introduced":["10.11.0+incompatible","11.4.0+incompatible","11.5.0+incompatible","11.6.0+incompatible"],"last_affected":[],"package":"github.com/mattermost/mattermost-server","purl":"pkg:golang/github.com/mattermost/mattermost-server","source":"GO-2026-5838"},{"ecosystem":"Go","fixed":["11.4.5"],"introduced":["11.4.0"],"last_affected":[],"package":"github.com/mattermost/mattermost-server","purl":null,"source":"GHSA-w9m8-p4cc-4qj9"},{"ecosystem":"Go","fixed":["11.4.5"],"introduced":["11.4.0"],"last_affected":[],"package":"github.com/mattermost/mattermost-server","purl":"pkg:golang/github.com/mattermost/mattermost-server","source":"GHSA-w9m8-p4cc-4qj9"},{"ecosystem":"Go","fixed":["11.5.4"],"introduced":["11.5.0"],"last_affected":[],"package":"github.com/mattermost/mattermost-server","purl":null,"source":"GHSA-w9m8-p4cc-4qj9"},{"ecosystem":"Go","fixed":["11.5.4"],"introduced":["11.5.0"],"last_affected":[],"package":"github.com/mattermost/mattermost-server","purl":"pkg:golang/github.com/mattermost/mattermost-server","source":"GHSA-w9m8-p4cc-4qj9"},{"ecosystem":"Go","fixed":["11.6.1"],"introduced":["11.6.0"],"last_affected":[],"package":"github.com/mattermost/mattermost-server","purl":null,"source":"GHSA-w9m8-p4cc-4qj9"},{"ecosystem":"Go","fixed":["11.6.1"],"introduced":["11.6.0"],"last_affected":[],"package":"github.com/mattermost/mattermost-server","purl":"pkg:golang/github.com/mattermost/mattermost-server","source":"GHSA-w9m8-p4cc-4qj9"},{"ecosystem":"Go","fixed":[],"introduced":["0"],"last_affected":[],"package":"github.com/mattermost/mattermost-server/v5","purl":"pkg:golang/github.com/mattermost/mattermost-server/v5","source":"GO-2026-5838"},{"ecosystem":"Go","fixed":[],"introduced":["0"],"last_affected":[],"package":"github.com/mattermost/mattermost-server/v6","purl":"pkg:golang/github.com/mattermost/mattermost-server/v6","source":"GO-2026-5838"},{"ecosystem":"Go","fixed":["8.0.0-20260410202636-17939826efa2"],"introduced":["0"],"last_affected":[],"package":"github.com/mattermost/mattermost/server/v8","purl":null,"source":"GHSA-w9m8-p4cc-4qj9"},{"ecosystem":"Go","fixed":["8.0.0-20260410202636-17939826efa2"],"introduced":["0"],"last_affected":[],"package":"github.com/mattermost/mattermost/server/v8","purl":"pkg:golang/github.com/mattermost/mattermost/server/v8","source":"GHSA-w9m8-p4cc-4qj9"},{"ecosystem":"Go","fixed":["8.0.0-20260410202636-17939826efa2"],"introduced":["0"],"last_affected":[],"package":"github.com/mattermost/mattermost/server/v8","purl":"pkg:golang/github.com/mattermost/mattermost/server/v8","source":"GO-2026-5838"}],"prev":{"headline":"PowerJob OpenAPI Endpoint addWorkflowNode GroovyEvaluator.evaluate code injection","id":"CVE-2026-5739"},"products":["Mattermost"],"published":"2026-05-22","related":[{"cvss_score":9.9,"headline":"Account takeover on OAuth/OpenID-enabled servers","id":"CVE-2025-12419","kev_date_added":null,"published":"2025-11-27"},{"cvss_score":9.9,"headline":"Account Takeover via Code Exchange Endpoint","id":"CVE-2025-12421","kev_date_added":null,"published":"2025-11-27"},{"cvss_score":9.9,"headline":"Path Traversal Leading to RCE by Any Authenticated Mattermost User","id":"CVE-2025-4981","kev_date_added":null,"published":"2025-06-20"},{"cvss_score":9.9,"headline":"Arbitrary file read via block duplication in Mattermost Boards","id":"CVE-2025-20051","kev_date_added":null,"published":"2025-02-24"},{"cvss_score":9.9,"headline":"Arbitrary file read in Mattermost Boards via import \u0026 export board archive","id":"CVE-2025-25279","kev_date_added":null,"published":"2025-02-24"},{"cvss_score":9.8,"headline":"Mattermost Server: Insufficient Password-Reset Link Invalidation","id":"CVE-2016-11074","kev_date_added":null,"published":"2020-06-19"},{"cvss_score":9.8,"headline":"Mattermost Server allows attackers to gain privileges by accessing unintended API endpoints with users' credentials","id":"CVE-2017-18885","kev_date_added":null,"published":"2020-06-19"}],"sources":[{"class":"attribution","licence":"CVE Terms of Use (MITRE)","name":"CVE List","prefix":"CVE"},{"class":"attribution","licence":"CC BY 4.0","name":"GitHub Advisory Database","prefix":"GHSA"},{"class":"attribution","licence":"CC BY 4.0","name":"Go Vulnerability Database","prefix":"GO"},{"class":"attribution","licence":"US public information, NVD API terms","name":"NVD"},{"class":"attribution","licence":"CWE Terms of Use","name":"CWE (MITRE)"},{"class":"attribution","licence":"FIRST CVSS licence","name":"CVSS (FIRST)"}],"ssvc":{"automatable":"yes","exploitation":"none","technical_impact":"partial"},"state":"PUBLISHED","updated":"2026-05-22","vendors":["Mattermost"]},"summary":"Unauthenticated attackers can crash the Mattermost server by sending crafted WebSocket messages, causing a full service outage.","url":"https://insights.sbomify.com/CVE-2026-5740/"}