Answer in brief
CVE-2026-77987 records a Critical severity (CVSS 9.3) vulnerability in GitHub Enterprise Server notebook viewer vulnerable to Server-side request forgery. The current sources do not mark it as known exploited. The current feed maps GitHub/Enterprise Server (generic). Check affected ranges and fixed versions before updating.
Analysis pending evidence review
HOL Guard separates source facts from reviewed analysis. See the methodology.
CVSS is 9.3. The current sources do not mark it as known exploited. Treat this as a source-backed prioritization signal, not a statement about your environment.
Analysis status
Analysis pending evidence review
Factual feed record only; HOL analysis is not approved for indexing. Read the methodology.
The current feed maps GitHub/Enterprise Server (generic). Check affected ranges and fixed versions before updating.
| Package | Affected range | Fixed version |
|---|---|---|
| GitHub/Enterprise Servergeneric | >=3.17.0 <3.17.* || >=3.18.0 <3.18.* || >=3.19.0 <3.19.* || >=3.20.0 <3.20.* || >=3.21.0 <3.21.* || >=3.22.0 <3.22.* | 3.17.*, 3.18.*, 3.19.*, 3.20.*, 3.21.*, 3.22.* |
Published upstream
Sep 22, 2026
Evidence: source:cvelist:source_dates:source-dates:recordSource modified
Sep 22, 2026
Evidence: source:cvelist:source_dates:source-dates:recordFirst seen by HOL
Sep 22, 2026
A server-side request forgery (SSRF) vulnerability was identified in the notebook viewer of GitHub Enterprise Server. The notebook viewer validated the scheme and host of a user-supplied URL but did not validate the port, allowing requests to be directed to internal services listening on other ports of the same appliance. Response bodies were not returned to the requester, but response timing acted as an oracle that allowed instance secrets to be extracted character by character. An extracted secret could then be used in a separate interaction with an internal service to obtain remote code execution on the appliance. Exploitation required network access to the instance and was unauthenticated when private mode was disabled, or required any authenticated user when private mode was enabled. This vulnerability affected GitHub Enterprise Server versions 3.17 through 3.22 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 through the GitHub Bug Bounty program.
Quoted source text, attributed separately from HOL analysis.