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CVE-2026-1355: Missing Authorization Check in GitHub Enterprise Server Allows Unauthorized Uploads to Repository Migration Exports

• Severity: medium (CVSS 6.5 v3.1)
• Exploited in the wild: not listed in CISA KEV
• EPSS: 0.5% probability of exploitation in the next 30 days
• Public exploit or detection template: none known
• Published: 2026-02-18 · updated 2026-06-17
• Weakness: CWE-862

Description

A Missing Authorization vulnerability was identified in GitHub Enterprise Server that allowed an attacker to upload unauthorized content to another user’s repository migration export due to a missing authorization check in the repository migration upload endpoint. By supplying the migration identifier, an attacker could overwrite or replace a victim’s migration archive, potentially causing victims to download attacker-controlled repository data during migration restores or automated imports. An attacker would require authentication to the victim's GitHub Enterprise Server instance. This vulnerability affected all versions of GitHub Enterprise Server prior to 3.20 and was fixed in versions 3.19.2, 3.18.5, 3.17.11, 3.16.14, 3.15.18, 3.14.23. This vulnerability was reported via the GitHub Bug Bounty program.

Affected products

• GitHub Enterprise Server: before 3.14.23; from 3.15.0 before 3.15.18; from 3.16.0 before 3.16.14; from 3.17.0 before 3.17.11; from 3.18.0 before 3.18.5; from 3.19.0 before 3.19.2 — fixed in 3.14.23, 3.15.18, 3.16.14, 3.17.11, 3.18.5, 3.19.2

How to fix

Upgrade to a fixed version: GitHub Enterprise Server 3.14.23, 3.15.18, 3.16.14, 3.17.11. Check the vendor advisory for mitigations.

References

• https://docs.github.com/en/enterprise-server@3.14/admin/release-notes#3.14.23
• https://docs.github.com/en/enterprise-server@3.15/admin/release-notes#3.15.18
• https://docs.github.com/en/enterprise-server@3.16/admin/release-notes#3.16.14
• https://docs.github.com/en/enterprise-server@3.17/admin/release-notes#3.17.11
• https://docs.github.com/en/enterprise-server@3.18/admin/release-notes#3.18.5
• https://docs.github.com/en/enterprise-server@3.19/admin/release-notes#3.19.2

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