CVE-2017-18877: Github.com/mattermost/mattermost server Cross-Site Scripting Vulnerability

MODERATE
Advisory Identifier: GHSA-9x8x-w6g5-hx4w
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CWE-79
Published
Advisory Summary

CVE-2017-18877 is a MODERATE cross-site scripting vulnerability (CWE-79: Improper Neutralization of Input During Web Page Generation ('Cross-site Scripting')) affecting Github.com/mattermost/mattermost server libraries in the Go ecosystem. The issue involves mattermost server is vulnerable to xss attacks against an oauth 2.0 allow/deny page. Remediation is available by upgrading affected packages to version 4.1.2, 4.2.1, 4.3.0.

CVE-2017-18877 at a Glance

CVE Identifier CVE-2017-18877
GHSA Identifier GHSA-9x8x-w6g5-hx4w
Severity MODERATE
CVSS v3.1 Base Score N/A
CWE Classification CWE-79: Improper Neutralization of Input During Web Page Generation ('Cross-site Scripting')
Affected Product Github.com/mattermost/mattermost server
Package Ecosystem Go
Published Date
Last Updated

How to Fix CVE-2017-18877

To remediate this vulnerability, upgrade all affected Github.com/mattermost/mattermost server dependencies to a patched release. Both direct and transitive dependencies should be checked, as frameworks or security libraries may pull in vulnerable versions transitively.

github.com/mattermost/mattermost-server fixed: 4.1.2 
Upgrade github.com/mattermost/mattermost-server to 4.1.2
github.com/mattermost/mattermost-server fixed: 4.2.1 
Upgrade github.com/mattermost/mattermost-server to 4.2.1
github.com/mattermost/mattermost-server fixed: 4.3.0 
Upgrade github.com/mattermost/mattermost-server to 4.3.0
Verify Direct and Transitive Dependencies

Run the following command in your project directory to verify that all resolved dependencies use the patched release: 

inspect dependencies for github.com/mattermost/mattermost-server

How to Check if You Are Affected

To determine whether your application is affected by CVE-2017-18877, inspect your project dependencies for Github.com/mattermost/mattermost server:

inspect dependencies for github.com/mattermost/mattermost-server

Analyze the terminal output to locate any version of Github.com/mattermost/mattermost server in your dependency tree. If any resolved version matches the vulnerable ranges listed in the table below (for example, versions earlier than 4.1.2), your application is affected.

Note: Verify declared build manifests and deployed runtime container environments.

Technical Details

Vulnerability Mechanism & Technical Analysis

This vulnerability is classified under CWE-79: Improper Neutralization of Input During Web Page Generation ('Cross-site Scripting'), where the product does not neutralize or incorrectly neutralizes user-controllable input before it is placed in output that is used as a web page that is served to other users. In Github.com/mattermost/mattermost server, software state validation or input boundaries are circumvented during processing. Review the official source advisory statement below for specific affected components, classes, and reproduction details.

Source Advisory Statement

An issue was discovered in Mattermost Server before 4.3.0, 4.2.1, and 4.1.2. XSS attacks could occur against an OAuth 2.0 allow/deny page.

CVE-2017-18877 Affected Github.com/mattermost/mattermost server Versions

3 component(s)
Fixed Versions:
4.1.24.2.14.3.0
Product / Package Ecosystem Affected Versions Fixed Version
github.com/mattermost/mattermost-server
golang/github.com/mattermost/mattermost-server
Go
< 4.1.2
4.1.2
github.com/mattermost/mattermost-server
golang/github.com/mattermost/mattermost-server
Go
≥ 4.2.0
< 4.2.1
4.2.1
github.com/mattermost/mattermost-server
golang/github.com/mattermost/mattermost-server
Go
≥ 4.3.0-rc1
< 4.3.0
4.3.0

References

NVD — CVE-2017-18877 NVD
https://nvd.nist.gov/vuln/detail/CVE-2017-18877
Github.com/mattermost/mattermost server Source Repository REPOSITORY
https://github.com/mattermost/mattermost
Github.com/mattermost/mattermost server Security Information SECURITY
https://mattermost.com/security-updates

Frequently Asked Questions

What is CVE-2017-18877?
CVE-2017-18877 is a security vulnerability in Github.com/mattermost/mattermost server involving Mattermost Server is vulnerable to XSS attacks against an OAuth 2.0 allow/deny page under CWE-79: Improper Neutralization of Input During Web Page Generation ('Cross-site Scripting').
Which Github.com/mattermost/mattermost server versions are affected?
Affected versions include releases prior to 4.1.2, 4.2.1, 4.3.0 across affected packages: github.com/mattermost/mattermost-server.
What version fixes CVE-2017-18877?
Upgrading to 4.1.2, 4.2.1, 4.3.0 (or the latest patched release for your respective branch) resolves the vulnerability.
Is github.com/mattermost/mattermost-server affected?
Yes, github.com/mattermost/mattermost-server is affected in releases prior to 4.1.2, 4.2.1, 4.3.0. Upgrade your dependency to 4.1.2, 4.2.1, 4.3.0 or later.
What CWE is associated with CVE-2017-18877?
CVE-2017-18877 is classified under CWE-79: Improper Neutralization of Input During Web Page Generation ('Cross-site Scripting') (The product does not neutralize or incorrectly neutralizes user-controllable input before it is placed in output that is used as a web page that is served to other users.).
How can I check Go dependencies for CVE-2017-18877?
Run the dependency tree command: 'inspect dependencies for github.com/mattermost/mattermost-server'. This command lists direct and transitive dependencies in your build configuration so you can verify if a vulnerable version is resolved.
Machine-readable OSV JSON OSV v1.5 Schema
Normalized schema output
View Raw JSON 
{
  "schema_version" : "1.4.0",
  "id" : "GHSA-9x8x-w6g5-hx4w",
  "modified" : "2025-12-05T15:10:38Z",
  "published" : "2022-05-24T17:21:03Z",
  "aliases" : [ "CVE-2017-18877" ],
  "summary" : "Mattermost Server is vulnerable to XSS attacks against an OAuth 2.0 allow/deny page",
  "details" : "An issue was discovered in Mattermost Server before 4.3.0, 4.2.1, and 4.1.2. XSS attacks could occur against an OAuth 2.0 allow/deny page.",
  "severity" : [ {
    "type" : "CVSS_V4",
    "score" : "CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:P/VC:N/VI:N/VA:N/SC:L/SI:L/SA:N"
  } ],
  "affected" : [ {
    "package" : {
      "ecosystem" : "Go",
      "name" : "github.com/mattermost/mattermost-server"
    },
    "ranges" : [ {
      "type" : "ECOSYSTEM",
      "events" : [ {
        "introduced" : "0"
      }, {
        "fixed" : "4.1.2"
      } ]
    } ]
  }, {
    "package" : {
      "ecosystem" : "Go",
      "name" : "github.com/mattermost/mattermost-server"
    },
    "ranges" : [ {
      "type" : "ECOSYSTEM",
      "events" : [ {
        "introduced" : "4.2.0"
      }, {
        "fixed" : "4.2.1"
      } ]
    } ]
  }, {
    "package" : {
      "ecosystem" : "Go",
      "name" : "github.com/mattermost/mattermost-server"
    },
    "ranges" : [ {
      "type" : "ECOSYSTEM",
      "events" : [ {
        "introduced" : "4.3.0-rc1"
      }, {
        "fixed" : "4.3.0"
      } ]
    } ]
  } ],
  "references" : [ {
    "type" : "ADVISORY",
    "url" : "https://nvd.nist.gov/vuln/detail/CVE-2017-18877"
  }, {
    "type" : "PACKAGE",
    "url" : "https://github.com/mattermost/mattermost"
  }, {
    "type" : "WEB",
    "url" : "https://mattermost.com/security-updates"
  } ],
  "database_specific" : {
    "cwe_ids" : [ "CWE-79" ],
    "severity" : "MODERATE",
    "github_reviewed" : true,
    "github_reviewed_at" : "2025-12-05T15:10:38Z",
    "nvd_published_at" : "2020-06-19T17:15:00Z"
  }
}