GHSA-c3mw-737p-c7g2: jupyter-server (CVE-2026-86049)

Package	Ecosystem	Affected	Fixed in
jupyter-server	PyPI	<2.21.0	2.21.0

Machine-written summary

Summary written by Claude Haiku from the source advisory. Not reviewed by a person.

Jupyter Server versions before 2.21.0 write request headers, including the Referer, into the server log when a request returns a 500, so a token carried in the Referer URL appears in plain text. An attacker who can read the server logs can extract those tokens, and the source notes that tokens reach the Referer during normal token-based login and launch flows. Upgrade jupyter-server to 2.21.0 or later. Until then, restrict who can read the server logs and avoid flows that place the token in the URL.

Written 1 Nov 2026.

Not analysed yet

We haven’t published our analysis of this Advisory yet. Once a person has reviewed it, this page will say what’s vulnerable, what has to be true for your app to be affected, and how to check.

Severity and exploitation

Score	Rating	CVSS	Vector	Source
7.1	High	3.1	CVSS:3.1/AV:N/AC:H/PR:L/UI:R/S:U/C:H/I:H/A:H	CNA (GitHub_M)

CISA KEV Not listed.
EPSS 0.0042, the 36th percentile, on 15 Nov 2026: FIRST’s estimate of the chance of exploitation in the next 30 days.

Timeline

31 Oct 2026, 14:09 UTC First seen by agentprime
31 Oct 2026, 14:09 UTC Confirmed by OSV

Sources

Facts on this page come from the GitHub Advisory Database (CC-BY 4.0), OSV and the other sources listed, as published. We don’t reproduce full advisory descriptions, which can contain exploit code.