Auth bypass in GitHub Enterprise Server
CVE-2026-1355
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.
Vulnerability class: Broken Access Control
Published · last modified .
CVSS v3 metric
CVSS v3 base score 6.5 (Medium). Vector: CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:N/I:H/A:N.
EPSS exploit prediction
EPSS: 0.004 (32.2th percentile), scored .
Very low probability of exploitation in the next 30 days; routine patching cadence is appropriate. 32nd percentile — 32.2% of CVEs in the catalogue have a lower EPSS than this one. How to read EPSS.
EPSS over last 30 days · oldest: 0.004 · newest: 0.004 · change: +0.000
Affected products
- GitHub Enterprise Server — versions 3.19.0, 3.18.0, 3.17.0
- GitHub Enterprise Server
Weakness classification (CWE)
References
- docs.github.com/en/enterprise-server@3.19/admin/release-notes (Product, Release Notes)
- docs.github.com/en/enterprise-server@3.18/admin/release-notes (Product, Release Notes)
- docs.github.com/en/enterprise-server@3.17/admin/release-notes (Product, Release Notes)
- docs.github.com/en/enterprise-server@3.16/admin/release-notes (Product, Release Notes)
- docs.github.com/en/enterprise-server@3.15/admin/release-notes (Product, Release Notes)
- docs.github.com/en/enterprise-server@3.14/admin/release-notes (Product, Release Notes)
Frequently asked questions
- What is CVE-2026-1355?
- CVE-2026-1355 is a medium-severity vulnerability in GitHub Enterprise Server, classified under Missing Authorization. CVSS score: 6.5/10. Published 2026-02-18.
- How severe is CVE-2026-1355?
- Medium severity. CVSS v3 base score is 6.5 out of 10.