{"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-2026-21386 in the wild and no public exploit code.","fix":"Upgrade github.com/mattermost/mattermost-server to a fixed version for your release line: 5.3.2-0.20260130144323-5bb5261c72fa, 10.11.11, 10.11.11+incompatible or 11.2.3+incompatible.","what":"CVE-2026-21386 is a medium-severity vulnerability in Mattermost Mattermost Server, published on 16 Mar 2026. Any signed-in user can exploit it over the network, with no action from the victim."},"fix_prompt":"Check this codebase for CVE-2026-21386 and fix it if it is affected.\n\nWhat it is: CVE-2026-21386 is a medium-severity vulnerability in Mattermost Mattermost Server, published on 16 Mar 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-2026-21386 in the wild and no public exploit code.\n\nAffected packages and fixed versions:\n- github.com/mattermost/mattermost-server (Go): affected all versions; fixed in 5.3.2-0.20260130144323-5bb5261c72fa\n- github.com/mattermost/mattermost-server (Go): affected all versions; fixed in 5.3.2-0.20260130144323-5bb5261c72fa\n- github.com/mattermost/mattermost-server (Go): affected from 10.11.0-rc1; fixed in 10.11.11\n- github.com/mattermost/mattermost-server (Go): affected from 10.11.0-rc1; fixed in 10.11.11\n- github.com/mattermost/mattermost-server (Go): affected from 10.11.0-rc1+incompatible; fixed in 10.11.11+incompatible, 11.2.3+incompatible, 11.3.1+incompatible\n- github.com/mattermost/mattermost-server (Go): affected from 11.2.0-rc1; fixed in 11.2.3\n- github.com/mattermost/mattermost-server (Go): affected from 11.2.0-rc1; fixed in 11.2.3\n- github.com/mattermost/mattermost-server (Go): affected from 11.3.0-rc1; fixed in 11.3.1\n- github.com/mattermost/mattermost-server (Go): affected from 11.3.0-rc1; fixed in 11.3.1\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 8.0.0-20260130144323-5bb5261c72fa\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-2026-21386/ (Markdown: https://insights.sbomify.com/CVE-2026-21386/index.md)","id":"CVE-2026-21386","markdown":"https://insights.sbomify.com/CVE-2026-21386/index.md","name":"CVE-2026-21386","record":{"aliases":["GHSA-5mr9-crcg-8wh2","GO-2026-4744"],"analysis":{"component_type":"web_application","fix_type":"upgrade","impacts":["data_read"],"network_reachable":"yes","non_default_config":false,"product_category":"Mattermost collaboration platform","requires_auth":"low_privilege","summary":"Authenticated users can enumerate private channels via inconsistent error messages in the /mute command, exposing unauthorized channel existence.","user_interaction":"not_required","vuln_class":"information_disclosure"},"analysis_generated_by":"qwen3.8-flash-next","assigner":"Mattermost","cpe":[{"product":"mattermost_server","vendor":"mattermost"}],"cvss":{"score":4.3,"severity":"medium","source":"cna","vector":"CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:L/I:N/A:N","version":"3.1"},"cwes":[{"id":"CWE-203","name":"Observable Discrepancy"}],"description":"Mattermost versions 11.3.x \u003c= 11.3.0, 11.2.x \u003c= 11.2.2, 10.11.x \u003c= 10.11.10 fail to use consistent error responses when handling the /mute command which allows an authenticated team member to enumerate private channels they are not authorized to know about via differing error messages for nonexistent versus private channels. Mattermost Advisory ID: MMSA-2026-00588","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":"Private channel enumeration via /mute slash command","id":"CVE-2026-21386","indexable":true,"kev":null,"kind":"cve","links":{"ecosystem":"Go","product":"mattermost:mattermost_server","products":["mattermost:mattermost_server"],"type":"information_disclosure","year":"2026"},"n_packages":14,"n_references":1,"next":{"headline":"Privilege escalation in Intel(R) LLM Library for PyTorch","id":"CVE-2026-21387"},"packages":[{"ecosystem":"Go","fixed":["5.3.2-0.20260130144323-5bb5261c72fa"],"introduced":["0"],"last_affected":[],"package":"github.com/mattermost/mattermost-server","purl":null,"source":"GHSA-5mr9-crcg-8wh2"},{"ecosystem":"Go","fixed":["5.3.2-0.20260130144323-5bb5261c72fa"],"introduced":["0"],"last_affected":[],"package":"github.com/mattermost/mattermost-server","purl":"pkg:golang/github.com/mattermost/mattermost-server","source":"GHSA-5mr9-crcg-8wh2"},{"ecosystem":"Go","fixed":["10.11.11"],"introduced":["10.11.0-rc1"],"last_affected":[],"package":"github.com/mattermost/mattermost-server","purl":null,"source":"GHSA-5mr9-crcg-8wh2"},{"ecosystem":"Go","fixed":["10.11.11"],"introduced":["10.11.0-rc1"],"last_affected":[],"package":"github.com/mattermost/mattermost-server","purl":"pkg:golang/github.com/mattermost/mattermost-server","source":"GHSA-5mr9-crcg-8wh2"},{"ecosystem":"Go","fixed":["10.11.11+incompatible","11.2.3+incompatible","11.3.1+incompatible"],"introduced":["10.11.0-rc1+incompatible","11.2.0-rc1+incompatible","11.3.0-rc1+incompatible"],"last_affected":[],"package":"github.com/mattermost/mattermost-server","purl":"pkg:golang/github.com/mattermost/mattermost-server","source":"GO-2026-4744"},{"ecosystem":"Go","fixed":["11.2.3"],"introduced":["11.2.0-rc1"],"last_affected":[],"package":"github.com/mattermost/mattermost-server","purl":null,"source":"GHSA-5mr9-crcg-8wh2"},{"ecosystem":"Go","fixed":["11.2.3"],"introduced":["11.2.0-rc1"],"last_affected":[],"package":"github.com/mattermost/mattermost-server","purl":"pkg:golang/github.com/mattermost/mattermost-server","source":"GHSA-5mr9-crcg-8wh2"},{"ecosystem":"Go","fixed":["11.3.1"],"introduced":["11.3.0-rc1"],"last_affected":[],"package":"github.com/mattermost/mattermost-server","purl":null,"source":"GHSA-5mr9-crcg-8wh2"},{"ecosystem":"Go","fixed":["11.3.1"],"introduced":["11.3.0-rc1"],"last_affected":[],"package":"github.com/mattermost/mattermost-server","purl":"pkg:golang/github.com/mattermost/mattermost-server","source":"GHSA-5mr9-crcg-8wh2"},{"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-2026-4744"},{"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-2026-4744"},{"ecosystem":"Go","fixed":["8.0.0-20260130144323-5bb5261c72fa"],"introduced":["0"],"last_affected":[],"package":"github.com/mattermost/mattermost/server/v8","purl":null,"source":"GHSA-5mr9-crcg-8wh2"},{"ecosystem":"Go","fixed":["8.0.0-20260130144323-5bb5261c72fa"],"introduced":["0"],"last_affected":[],"package":"github.com/mattermost/mattermost/server/v8","purl":"pkg:golang/github.com/mattermost/mattermost/server/v8","source":"GHSA-5mr9-crcg-8wh2"},{"ecosystem":"Go","fixed":["8.0.0-20260130144323-5bb5261c72fa"],"introduced":["0"],"last_affected":[],"package":"github.com/mattermost/mattermost/server/v8","purl":"pkg:golang/github.com/mattermost/mattermost/server/v8","source":"GO-2026-4744"}],"prev":{"headline":"Qualcomm Multiple Chipsets Memory Corruption","id":"CVE-2026-21385"},"products":["Mattermost"],"published":"2026-03-16","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":"2026-03-16","vendors":["Mattermost"]},"summary":"Authenticated users can enumerate private channels via inconsistent error messages in the /mute command, exposing unauthorized channel existence.","url":"https://insights.sbomify.com/CVE-2026-21386/"}