# CVE-2025-21088: WebApp crash via improper validation of proto style in attachments > An attacker can crash the Mattermost web frontend by sending crafted malicious input in post attachments, requiring an upgrade to fix. - **Severity:** Medium 6.5 (`CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H`) - **Exploited in the wild:** Not known - **Login needed:** Any signed-in user - **Attackable:** Over the internet - **Victim action needed:** Not needed - **Fix available:** Yes - **Published:** 15 Jan 2025 - **Updated:** 15 Jan 2025 - **Also known as:** GHSA-8j3q-gc9x-7972, GO-2025-3393 ## What is CVE-2025-21088? CVE-2025-21088 is a medium-severity denial of service vulnerability in Mattermost Mattermost Server, published on 15 Jan 2025. Any signed-in user can exploit it over the network, with no action from the victim. ### Official description Mattermost versions 10.2.x <= 10.2.0, 9.11.x <= 9.11.5, 10.0.x <= 10.0.3, 10.1.x <= 10.1.3 fail to properly validate the style of proto supplied to an action's style in post.props.attachments, which allows an attacker to crash the frontend via crafted malicious input. Weakness: CWE-704 (Incorrect Type Conversion or Cast) ## Which versions are affected by CVE-2025-21088? 14 open source packages ship an affected version, including github.com/mattermost/mattermost/server/v8, github.com/mattermost/mattermost-server and github.com/mattermost/mattermost-server/v5. It affects 1 product. | Package | Ecosystem | Affected | Fixed in | | --- | --- | --- | --- | | `github.com/mattermost/mattermost/server/v8` | Go | All versions | 8.0.0-20241127161322-25ff7a3779a5 | | `github.com/mattermost/mattermost/server/v8` | Go | All versions | 8.0.0-20241127161322-25ff7a3779a5 | | `github.com/mattermost/mattermost/server/v8` | Go | All versions | 8.0.0-20241127161322-25ff7a3779a5 | | `github.com/mattermost/mattermost/server/v8` | Go | From 10.0.0 | 10.0.4 | | `github.com/mattermost/mattermost/server/v8` | Go | From 10.0.0 | 10.0.4 | | `github.com/mattermost/mattermost/server/v8` | Go | From 10.1.0 | 10.1.4 | | `github.com/mattermost/mattermost/server/v8` | Go | From 10.1.0 | 10.1.4 | | `github.com/mattermost/mattermost/server/v8` | Go | From 10.2.0 | 10.2.1 | | `github.com/mattermost/mattermost/server/v8` | Go | From 10.2.0 | 10.2.1 | | `github.com/mattermost/mattermost/server/v8` | Go | From 9.11.0 | 9.11.6 | | `github.com/mattermost/mattermost/server/v8` | Go | From 9.11.0 | 9.11.6 | | `github.com/mattermost/mattermost-server` | Go | From 9.11.0+incompatible | 9.11.6+incompatible, 10.0.4+incompatible, 10.1.4+incompatible, 10.2.1+incompatible | | `github.com/mattermost/mattermost-server/v5` | Go | All versions | None | | `github.com/mattermost/mattermost-server/v6` | Go | All versions | None | Products: Mattermost Mattermost Server. ## How do I fix CVE-2025-21088? Upgrade github.com/mattermost/mattermost/server/v8 to a fixed version for your release line: 8.0.0-20241127161322-25ff7a3779a5, 10.0.4, 10.1.4 or 10.2.1. ## Is CVE-2025-21088 being exploited? There is no known exploitation of CVE-2025-21088 in the wild and no public exploit code. ## Other vulnerabilities in Mattermost Mattermost Server - [CVE-2025-12419](https://insights.sbomify.com/CVE-2025-12419/): Account takeover on OAuth/OpenID-enabled servers (critical 9.9) - [CVE-2025-12421](https://insights.sbomify.com/CVE-2025-12421/): Account Takeover via Code Exchange Endpoint (critical 9.9) - [CVE-2025-4981](https://insights.sbomify.com/CVE-2025-4981/): Path Traversal Leading to RCE by Any Authenticated Mattermost User (critical 9.9) - [CVE-2025-20051](https://insights.sbomify.com/CVE-2025-20051/): Arbitrary file read via block duplication in Mattermost Boards (critical 9.9) - [CVE-2025-25279](https://insights.sbomify.com/CVE-2025-25279/): Arbitrary file read in Mattermost Boards via import & export board archive (critical 9.9) ## Fix prompt for AI coding agents ```text Check this codebase for CVE-2025-21088 and fix it if it is affected. What it is: CVE-2025-21088 is a medium-severity denial of service vulnerability in Mattermost Mattermost Server, published on 15 Jan 2025. Any signed-in user can exploit it over the network, with no action from the victim. Exploitation: There is no known exploitation of CVE-2025-21088 in the wild and no public exploit code. Affected packages and fixed versions: - github.com/mattermost/mattermost/server/v8 (Go): affected all versions; fixed in 8.0.0-20241127161322-25ff7a3779a5 - github.com/mattermost/mattermost/server/v8 (Go): affected all versions; fixed in 8.0.0-20241127161322-25ff7a3779a5 - github.com/mattermost/mattermost/server/v8 (Go): affected all versions; fixed in 8.0.0-20241127161322-25ff7a3779a5 - github.com/mattermost/mattermost/server/v8 (Go): affected from 10.0.0; fixed in 10.0.4 - github.com/mattermost/mattermost/server/v8 (Go): affected from 10.0.0; fixed in 10.0.4 - github.com/mattermost/mattermost/server/v8 (Go): affected from 10.1.0; fixed in 10.1.4 - github.com/mattermost/mattermost/server/v8 (Go): affected from 10.1.0; fixed in 10.1.4 - github.com/mattermost/mattermost/server/v8 (Go): affected from 10.2.0; fixed in 10.2.1 - github.com/mattermost/mattermost/server/v8 (Go): affected from 10.2.0; fixed in 10.2.1 - github.com/mattermost/mattermost/server/v8 (Go): affected from 9.11.0; fixed in 9.11.6 - github.com/mattermost/mattermost/server/v8 (Go): affected from 9.11.0; fixed in 9.11.6 - github.com/mattermost/mattermost-server (Go): affected from 9.11.0+incompatible; fixed in 9.11.6+incompatible, 10.0.4+incompatible, 10.1.4+incompatible, 10.2.1+incompatible Task: 1. 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. 2. 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. 3. If there is no fix, or the upgrade would break the build, do not guess: explain the risk and the safest workaround instead. 4. Run the tests and summarise what changed and why. 5. If nothing in the project is affected, say so and change nothing. Reference: https://insights.sbomify.com/CVE-2025-21088/ (Markdown: https://insights.sbomify.com/CVE-2025-21088/index.md) ``` ## Sources - CVE record: https://www.cve.org/CVERecord?id=CVE-2025-21088 - NVD: https://nvd.nist.gov/vuln/detail/CVE-2025-21088 - OSV: https://osv.dev/vulnerability/CVE-2025-21088 --- From sbomify Insights: https://insights.sbomify.com/CVE-2025-21088/ Summaries are generated and may contain mistakes; the official description above is the record.