{"answers":{"affected":"7 open source packages ship an affected version, including github.com/mattermost/mattermost-server. It affects 1 product.","exploited":"There is no known exploitation of CVE-2026-4054 in the wild and no public exploit code.","fix":"Upgrade github.com/mattermost/mattermost-server to a fixed version for your release line: 0.0.0-20260414103857-b21ef302025e, 11.4.4+incompatible, 11.5.2+incompatible or 11.4.4.","what":"CVE-2026-4054 is a medium-severity denial of service vulnerability in Mattermost Mattermost Server, published on 15 May 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-2026-4054 and fix it if it is affected.\n\nWhat it is: CVE-2026-4054 is a medium-severity denial of service vulnerability in Mattermost Mattermost Server, published on 15 May 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-2026-4054 in the wild and no public exploit code.\n\nAffected packages and fixed versions:\n- github.com/mattermost/mattermost-server (Go): affected from 0.0.0-20250731163400-5b955468ea1e; fixed in 0.0.0-20260414103857-b21ef302025e, 11.4.4+incompatible, 11.5.2+incompatible\n- github.com/mattermost/mattermost-server (Go): affected from 0.0.0-20250731163400-5b955468ea1e; fixed in 0.0.0-20260414103857-b21ef302025e\n- github.com/mattermost/mattermost-server (Go): affected from 0.0.0-20250731163400-5b955468ea1e; fixed in 0.0.0-20260414103857-b21ef302025e\n- github.com/mattermost/mattermost-server (Go): affected from 11.4.0; fixed in 11.4.4\n- github.com/mattermost/mattermost-server (Go): affected from 11.4.0; fixed in 11.4.4\n- github.com/mattermost/mattermost-server (Go): affected from 11.5.0; fixed in 11.5.2\n- github.com/mattermost/mattermost-server (Go): affected from 11.5.0; fixed in 11.5.2\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-2026-4054/ (Markdown: https://insights.sbomify.com/CVE-2026-4054/index.md)","id":"CVE-2026-4054","markdown":"https://insights.sbomify.com/CVE-2026-4054/index.md","name":"CVE-2026-4054","record":{"aliases":["GHSA-j76w-p754-g2w7","GO-2026-5454"],"analysis":{"component_type":"web_application","fix_type":"upgrade","impacts":["denial_of_service"],"network_reachable":"yes","non_default_config":false,"product_category":"Mattermost collaboration platform","requires_auth":"none","summary":"Remote attackers can cause client-side denial of service by serving malicious SVG files through the image proxy with spoofed Content-Type headers.","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":4.3,"severity":"medium","source":"cna","vector":"CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:N/I:N/A:L","version":"3.1"},"cwes":[{"id":"CWE-754","name":"Improper Check for Unusual or Exceptional Conditions"}],"description":"Mattermost versions 11.5.x \u003c= 11.5.1, 10.11.x \u003c= 10.11.13, 11.4.x \u003c= 11.4.3 Fail to validate the response body of proxied images, which allows a remote attacker to enact client-side DoS via an SVG file served from an attacker-controlled origin under a non-SVG Content-Type header (e.g. image/png) embedded in an og:image meta tag or Markdown image link.. Mattermost Advisory ID: MMSA-2026-00630","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":"Mattermost doesn't validate the response body of proxied images","id":"CVE-2026-4054","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":7,"n_references":1,"next":{"headline":"Insufficient permission validation on cross-team playbook run creation","id":"CVE-2026-4055"},"packages":[{"ecosystem":"Go","fixed":["0.0.0-20260414103857-b21ef302025e","11.4.4+incompatible","11.5.2+incompatible"],"introduced":["0.0.0-20250731163400-5b955468ea1e","11.4.0+incompatible","11.5.0+incompatible"],"last_affected":[],"package":"github.com/mattermost/mattermost-server","purl":"pkg:golang/github.com/mattermost/mattermost-server","source":"GO-2026-5454"},{"ecosystem":"Go","fixed":["0.0.0-20260414103857-b21ef302025e"],"introduced":["0.0.0-20250731163400-5b955468ea1e"],"last_affected":[],"package":"github.com/mattermost/mattermost-server","purl":null,"source":"GHSA-j76w-p754-g2w7"},{"ecosystem":"Go","fixed":["0.0.0-20260414103857-b21ef302025e"],"introduced":["0.0.0-20250731163400-5b955468ea1e"],"last_affected":[],"package":"github.com/mattermost/mattermost-server","purl":"pkg:golang/github.com/mattermost/mattermost-server","source":"GHSA-j76w-p754-g2w7"},{"ecosystem":"Go","fixed":["11.4.4"],"introduced":["11.4.0"],"last_affected":[],"package":"github.com/mattermost/mattermost-server","purl":null,"source":"GHSA-j76w-p754-g2w7"},{"ecosystem":"Go","fixed":["11.4.4"],"introduced":["11.4.0"],"last_affected":[],"package":"github.com/mattermost/mattermost-server","purl":"pkg:golang/github.com/mattermost/mattermost-server","source":"GHSA-j76w-p754-g2w7"},{"ecosystem":"Go","fixed":["11.5.2"],"introduced":["11.5.0"],"last_affected":[],"package":"github.com/mattermost/mattermost-server","purl":null,"source":"GHSA-j76w-p754-g2w7"},{"ecosystem":"Go","fixed":["11.5.2"],"introduced":["11.5.0"],"last_affected":[],"package":"github.com/mattermost/mattermost-server","purl":"pkg:golang/github.com/mattermost/mattermost-server","source":"GHSA-j76w-p754-g2w7"}],"prev":{"headline":"post edit time limit is not enforced on some post update operations","id":"CVE-2026-4053"},"products":["Mattermost"],"published":"2026-05-15","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":"2026-05-15","vendors":["Mattermost"]},"summary":"Remote attackers can cause client-side denial of service by serving malicious SVG files through the image proxy with spoofed Content-Type headers.","url":"https://insights.sbomify.com/CVE-2026-4054/"}