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Enterprise Server · cross-site scripting

CVSS 4.0 7.4 HIGHCheck source for fixed versionsKEV status unknown

cve-program · CVE-2026-77912

Published

A stored cross-site scripting (XSS) vulnerability was identified in GitHub Enterprise Server that allowed an authenticated attacker to inject arbitrary HTML attributes into rendered Markdown because the Markdown rendering pipeline rewrote quote characters in already-sanitized HTML without re-sanitizing the result. Crafted Markdown could abuse same-origin JavaScript gadgets to bypass Content Security Policy and gain control of the page DOM when viewed by another user. Successful exploitation could allow an attacker to read content visible to the victim, extract embedded CSRF tokens, perform state-changing actions as the victim, and exfiltrate data through same-origin writes. The payload could also propagate to repositories and organizations where the victim had write access. This vulnerability affected supported GitHub Enterprise Server releases in the 3.17, 3.18, 3.19, 3.20, 3.21, and 3.22 series and was fixed in versions 3.22.1, 3.21.6, 3.20.8, 3.19.12, 3.18.15, and 3.17.21. This vulnerability was reported via the GitHub Bug Bounty program.

Read the publisher's advisory

Affected versions, risk and source history

cve-program · CVE-2026-77912

Published

Enterprise Server

Vendor product

Publisher's version information

Shown as published. These rules are not interpreted as NuGet package version ranges.

{
                    "vendor": "GitHub",
                    "product": "Enterprise Server",
                    "versions": [
                        {
                            "status": "affected",
                            "version": "3.17.0",
                            "lessThan": "3.17.*",
                            "changes": [
                                {
                                    "at": "3.17.21",
                                    "status": "unaffected"
                                }
                            ],
                            "versionType": "semver"
                        },
                        {
                            "status": "affected",
                            "version": "3.18.0",
                            "lessThan": "3.18.*",
                            "changes": [
                                {
                                    "at": "3.18.15",
                                    "status": "unaffected"
                                }
                            ],
                            "versionType": "semver"
                        },
                        {
                            "status": "affected",
                            "version": "3.19.0",
                            "lessThan": "3.19.*",
                            "changes": [
                                {
                                    "at": "3.19.12",
                                    "status": "unaffected"
                                }
                            ],
                            "versionType": "semver"
                        },
                        {
                            "status": "affected",
                            "version": "3.20.0",
                            "lessThan": "3.20.*",
                            "changes": [
                                {
                                    "at": "3.20.8",
                                    "status": "unaffected"
                                }
                            ],
                            "versionType": "semver"
                        },
                        {
                            "status": "affected",
                            "version": "3.21.0",
                            "lessThan": "3.21.*",
                            "changes": [
                                {
                                    "at": "3.21.6",
                                    "status": "unaffected"
                                }
                            ],
                            "versionType": "semver"
                        },
                        {
                            "status": "affected",
                            "version": "3.22.0",
                            "lessThan": "3.22.*",
                            "changes": [
                                {
                                    "at": "3.22.1",
                                    "status": "unaffected"
                                }
                            ],
                            "versionType": "semver"
                        }
                    ],
                    "defaultStatus": "unknown"
                }

Original source record · Cite this exact observation · Complete original publisher JSON

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