{"answers":{"affected":"17 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-2026-0999 in the wild and no public exploit code.","fix":"Upgrade github.com/mattermost/mattermost-server to 5.3.2-0.20251212052346-61651b0df7ea or later.","what":"CVE-2026-0999 is a medium-severity authentication bypass vulnerability in Mattermost Mattermost Server, published on 16 Feb 2026. Any signed-in user can exploit it over the network, with no action from the victim."},"fix_prompt":"Check this codebase for CVE-2026-0999 and fix it if it is affected.\n\nWhat it is: CVE-2026-0999 is a medium-severity authentication bypass vulnerability in Mattermost Mattermost Server, published on 16 Feb 2026. Any signed-in user can exploit it over the network, with no action from the victim.\nExploitation: There is no known exploitation of CVE-2026-0999 in the wild and no public exploit code.\n\nAffected packages and fixed versions:\n- github.com/mattermost/mattermost-server (Go): affected all versions; no fix listed\n- github.com/mattermost/mattermost-server (Go): affected all versions; fixed in 5.3.2-0.20251212052346-61651b0df7ea\n- github.com/mattermost/mattermost-server (Go): affected all versions; fixed in 5.3.2-0.20251212052346-61651b0df7ea\n- github.com/mattermost/mattermost-server (Go): affected from 10.11.0; no fix listed\n- github.com/mattermost/mattermost-server (Go): affected from 10.11.0; no fix listed\n- github.com/mattermost/mattermost-server (Go): affected from 10.11.0+incompatible; no fix listed\n- github.com/mattermost/mattermost-server (Go): affected from 11.1.0; no fix listed\n- github.com/mattermost/mattermost-server (Go): affected from 11.1.0; no fix listed\n- github.com/mattermost/mattermost-server (Go): affected from 11.1.0+incompatible; no fix listed\n- github.com/mattermost/mattermost-server (Go): affected from 11.2.0; no fix listed\n- github.com/mattermost/mattermost-server (Go): affected from 11.2.0; no fix listed\n- github.com/mattermost/mattermost-server (Go): affected from 11.2.0+incompatible; no fix listed\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-2026-0999/ (Markdown: https://insights.sbomify.com/CVE-2026-0999/index.md)","id":"CVE-2026-0999","markdown":"https://insights.sbomify.com/CVE-2026-0999/index.md","name":"CVE-2026-0999","record":{"aliases":["GHSA-3c9r-7f29-qp32","GO-2026-4520"],"analysis":{"component_type":"web_application","fix_type":"upgrade","impacts":["security_bypass"],"network_reachable":"yes","non_default_config":true,"product_category":"Mattermost collaboration platform","requires_auth":"low_privilege","summary":"Authenticated users can bypass SSO-only login restrictions by using userID-based authentication when email and username logins are disabled.","user_interaction":"not_required","vuln_class":"auth_bypass"},"analysis_generated_by":"qwen3.8-flash-next","assigner":"Mattermost","cpe":[{"product":"mattermost_server","vendor":"mattermost"}],"cvss":{"score":5.4,"severity":"medium","source":"cna","vector":"CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:L/I:L/A:N","version":"3.1"},"cwes":[{"id":"CWE-303","name":"Incorrect Implementation of Authentication Algorithm"}],"description":"Mattermost versions 11.1.x \u003c= 11.1.2, 10.11.x \u003c= 10.11.9, 11.2.x \u003c= 11.2.1 fail to properly validate login method restrictions which allows an authenticated user to bypass SSO-only login requirements via userID-based authentication. Mattermost Advisory ID: MMSA-2025-00548","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":"Authentication bypass via userID login when email and username login are disabled","id":"CVE-2026-0999","indexable":true,"kev":null,"kind":"cve","links":{"ecosystem":"Go","product":"mattermost:mattermost_server","products":["mattermost:mattermost_server"],"type":"auth_bypass","year":"2026"},"n_packages":17,"n_references":1,"next":{"headline":"MailerLite - WooCommerce integration \u003c= 3.1.3 - Missing Authorization to Data Deletion","id":"CVE-2026-1000"},"packages":[{"ecosystem":"Go","fixed":[],"introduced":["0"],"last_affected":[],"package":"github.com/mattermost/mattermost-server","purl":"pkg:golang/github.com/mattermost/mattermost-server","source":"GO-2026-4520"},{"ecosystem":"Go","fixed":["5.3.2-0.20251212052346-61651b0df7ea"],"introduced":["0"],"last_affected":[],"package":"github.com/mattermost/mattermost-server","purl":null,"source":"GHSA-3c9r-7f29-qp32"},{"ecosystem":"Go","fixed":["5.3.2-0.20251212052346-61651b0df7ea"],"introduced":["0"],"last_affected":[],"package":"github.com/mattermost/mattermost-server","purl":"pkg:golang/github.com/mattermost/mattermost-server","source":"GHSA-3c9r-7f29-qp32"},{"ecosystem":"Go","fixed":[],"introduced":["10.11.0"],"last_affected":[],"package":"github.com/mattermost/mattermost-server","purl":null,"source":"GHSA-3c9r-7f29-qp32"},{"ecosystem":"Go","fixed":[],"introduced":["10.11.0"],"last_affected":[],"package":"github.com/mattermost/mattermost-server","purl":"pkg:golang/github.com/mattermost/mattermost-server","source":"GHSA-3c9r-7f29-qp32"},{"ecosystem":"Go","fixed":[],"introduced":["10.11.0+incompatible"],"last_affected":[],"package":"github.com/mattermost/mattermost-server","purl":"pkg:golang/github.com/mattermost/mattermost-server","source":"GO-2026-4520"},{"ecosystem":"Go","fixed":[],"introduced":["11.1.0"],"last_affected":[],"package":"github.com/mattermost/mattermost-server","purl":null,"source":"GHSA-3c9r-7f29-qp32"},{"ecosystem":"Go","fixed":[],"introduced":["11.1.0"],"last_affected":[],"package":"github.com/mattermost/mattermost-server","purl":"pkg:golang/github.com/mattermost/mattermost-server","source":"GHSA-3c9r-7f29-qp32"},{"ecosystem":"Go","fixed":[],"introduced":["11.1.0+incompatible"],"last_affected":[],"package":"github.com/mattermost/mattermost-server","purl":"pkg:golang/github.com/mattermost/mattermost-server","source":"GO-2026-4520"},{"ecosystem":"Go","fixed":[],"introduced":["11.2.0"],"last_affected":[],"package":"github.com/mattermost/mattermost-server","purl":null,"source":"GHSA-3c9r-7f29-qp32"},{"ecosystem":"Go","fixed":[],"introduced":["11.2.0"],"last_affected":[],"package":"github.com/mattermost/mattermost-server","purl":"pkg:golang/github.com/mattermost/mattermost-server","source":"GHSA-3c9r-7f29-qp32"},{"ecosystem":"Go","fixed":[],"introduced":["11.2.0+incompatible"],"last_affected":[],"package":"github.com/mattermost/mattermost-server","purl":"pkg:golang/github.com/mattermost/mattermost-server","source":"GO-2026-4520"},{"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-2026-4520"},{"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-2026-4520"},{"ecosystem":"Go","fixed":["8.0.0-20251212052346-61651b0df7ea"],"introduced":["0"],"last_affected":[],"package":"github.com/mattermost/mattermost/server/v8","purl":null,"source":"GHSA-3c9r-7f29-qp32"},{"ecosystem":"Go","fixed":["8.0.0-20251212052346-61651b0df7ea"],"introduced":["0"],"last_affected":[],"package":"github.com/mattermost/mattermost/server/v8","purl":"pkg:golang/github.com/mattermost/mattermost/server/v8","source":"GHSA-3c9r-7f29-qp32"},{"ecosystem":"Go","fixed":["8.0.0-20251212052346-61651b0df7ea"],"introduced":["0"],"last_affected":[],"package":"github.com/mattermost/mattermost/server/v8","purl":"pkg:golang/github.com/mattermost/mattermost/server/v8","source":"GO-2026-4520"}],"prev":{"headline":"Mattermost Zoom Plugin allows unauthorized meeting creation and post modification via insufficient API access controls","id":"CVE-2026-0998"},"products":["Mattermost"],"published":"2026-02-16","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":"no","exploitation":"none","technical_impact":"partial"},"state":"PUBLISHED","updated":"2026-02-17","vendors":["Mattermost"]},"summary":"Authenticated users can bypass SSO-only login restrictions by using userID-based authentication when email and username logins are disabled.","url":"https://insights.sbomify.com/CVE-2026-0999/"}