{"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-2026-2456 in the wild and no public exploit code.","fix":"Upgrade github.com/mattermost/mattermost-server to a fixed version for your release line: 5.3.2-0.20260127165411-fe3052073dc6, 10.11.11, 10.11.11+incompatible or 11.2.3+incompatible.","what":"CVE-2026-2456 is a medium-severity denial of service vulnerability in Mattermost Mattermost Server, published on 16 Mar 2026. An attacker can exploit it over the internet without logging in, and only if a user opens a file or follows a link."},"fix_prompt":"Check this codebase for CVE-2026-2456 and fix it if it is affected.\n\nWhat it is: CVE-2026-2456 is a medium-severity denial of service vulnerability in Mattermost Mattermost Server, published on 16 Mar 2026. An attacker can exploit it over the internet without logging in, and only if a user opens a file or follows a link.\nExploitation: There is no known exploitation of CVE-2026-2456 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 5.3.2-0.20260127165411-fe3052073dc6\n- github.com/mattermost/mattermost-server (Go): affected all versions; fixed in 5.3.2-0.20260127165411-fe3052073dc6\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 8.0.0-20260127165411-fe3052073dc6\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-2026-2456/ (Markdown: https://insights.sbomify.com/CVE-2026-2456/index.md)","id":"CVE-2026-2456","markdown":"https://insights.sbomify.com/CVE-2026-2456/index.md","name":"CVE-2026-2456","record":{"aliases":["GHSA-34g8-9fpp-46ch","GO-2026-4726"],"analysis":{"component_type":"web_application","fix_type":"upgrade","impacts":["denial_of_service"],"network_reachable":"yes","non_default_config":false,"product_category":"Mattermost chat platform","requires_auth":"none","summary":"An authenticated attacker can cause server memory exhaustion and denial of service by configuring a malicious integration server to return large responses.","user_interaction":"required","vuln_class":"denial_of_service"},"analysis_generated_by":"qwen3.8-flash-next","assigner":"Mattermost","cpe":[{"product":"mattermost_server","vendor":"mattermost"}],"cvss":{"score":5.3,"severity":"medium","source":"cna","vector":"CVSS:3.1/AV:N/AC:H/PR:N/UI:R/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 11.3.x \u003c= 11.3.0, 11.2.x \u003c= 11.2.2, 10.11.x \u003c= 10.11.10 Mattermost fails to limit the size of responses from integration action endpoints, which allows an authenticated attacker to cause server memory exhaustion and denial of service via a malicious integration server that returns an arbitrarily large response when a user clicks an interactive message button.. Mattermost Advisory ID: MMSA-2026-00571","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":"Denial of Service via Unbounded Memory Allocation in Integration Actions","id":"CVE-2026-2456","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":"WebSocket Message Spoofing via Permalink Embed Manipulation","id":"CVE-2026-2457"},"packages":[{"ecosystem":"Go","fixed":["5.3.2-0.20260127165411-fe3052073dc6"],"introduced":["0"],"last_affected":[],"package":"github.com/mattermost/mattermost-server","purl":null,"source":"GHSA-34g8-9fpp-46ch"},{"ecosystem":"Go","fixed":["5.3.2-0.20260127165411-fe3052073dc6"],"introduced":["0"],"last_affected":[],"package":"github.com/mattermost/mattermost-server","purl":"pkg:golang/github.com/mattermost/mattermost-server","source":"GHSA-34g8-9fpp-46ch"},{"ecosystem":"Go","fixed":["10.11.11"],"introduced":["10.11.0-rc1"],"last_affected":[],"package":"github.com/mattermost/mattermost-server","purl":null,"source":"GHSA-34g8-9fpp-46ch"},{"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-34g8-9fpp-46ch"},{"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-2026-4726"},{"ecosystem":"Go","fixed":["11.2.3"],"introduced":["11.2.0-rc1"],"last_affected":[],"package":"github.com/mattermost/mattermost-server","purl":null,"source":"GHSA-34g8-9fpp-46ch"},{"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-34g8-9fpp-46ch"},{"ecosystem":"Go","fixed":["11.3.1"],"introduced":["11.3.0-rc1"],"last_affected":[],"package":"github.com/mattermost/mattermost-server","purl":null,"source":"GHSA-34g8-9fpp-46ch"},{"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-34g8-9fpp-46ch"},{"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-2026-4726"},{"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-2026-4726"},{"ecosystem":"Go","fixed":["8.0.0-20260127165411-fe3052073dc6"],"introduced":["0"],"last_affected":[],"package":"github.com/mattermost/mattermost/server/v8","purl":null,"source":"GHSA-34g8-9fpp-46ch"},{"ecosystem":"Go","fixed":["8.0.0-20260127165411-fe3052073dc6"],"introduced":["0"],"last_affected":[],"package":"github.com/mattermost/mattermost/server/v8","purl":"pkg:golang/github.com/mattermost/mattermost/server/v8","source":"GHSA-34g8-9fpp-46ch"},{"ecosystem":"Go","fixed":["8.0.0-20260127165411-fe3052073dc6"],"introduced":["0"],"last_affected":[],"package":"github.com/mattermost/mattermost/server/v8","purl":"pkg:golang/github.com/mattermost/mattermost/server/v8","source":"GO-2026-4726"}],"prev":{"headline":"SSRF bypass via IPv4-mapped IPv6 literals","id":"CVE-2026-2455"},"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":"An authenticated attacker can cause server memory exhaustion and denial of service by configuring a malicious integration server to return large responses.","url":"https://insights.sbomify.com/CVE-2026-2456/"}