jupyter_server: Insertion of Sensitive Information into Log File
CVE-2026-86049 is a high-severity insertion of sensitive information into log file vulnerability in jupyter_server from Jupyter-server, with a CVSS 3.1 base score of 7.1 out of 10. It can be exploited remotely over the network by an attacker with a low-privileged account, but only if a user takes part, for example by opening a link or file. Affected jupyter_server versions: < 2.21.0. The record does not name a fixed version, so check the vendor advisory. There is no confirmed exploitation so far. EPSS estimates a 0.42% chance of exploitation within 30 days, which is low compared with other CVEs.
High severity with no evidence of exploitation so far.
What to do
- Check which version of jupyter_server you run against the affected versions below, and install the vendor's latest release.
- Read the advisory on github.com for workarounds and exact fixed builds.
- Because the attack needs a user to take part, warn users about unexpected links and files related to this product until it is patched.
Affected products and versions
| Vendor | Product | Affected versions | Fixed in |
|---|---|---|---|
| Jupyter-server | jupyter_server | < 2.21.0 | Not stated |
Version data comes from the organisation that assigned the CVE. Confirm against the vendor advisory before deciding you are unaffected.
How the severity score breaks down
- Attack vector
- NetworkCan be exploited remotely over a network, including the internet.
- Attack complexity
- HighSuccess depends on conditions outside the attacker's control.
- Privileges required
- LowA basic user account is enough.
- User interaction
- RequiredA user must take an action such as opening a file or link.
- Scope
- UnchangedImpact stays within the vulnerable component.
- Confidentiality
- HighAll data handled by the component can be read.
- Integrity
- HighData or code can be modified at will.
- Availability
- HighThe component can be taken down completely.
Vector: CVSS:3.1/AV:N/AC:H/PR:L/UI:R/S:U/C:H/I:H/A:H. Scored by CNA (github.com).
Official description
Jupyter Server is the backend for Jupyter web applications. Prior to version 2.21.0, the 5xx request logging path in jupyter_server/log.py copies the Referer header into a JSON header block without applying the token scrubbing used for the request URI. A request that returns HTTP 500 while the Referer contains a token-bearing URL can therefore write that token to server logs in plaintext. An attacker who can read those logs can recover the token and use the affected user's Jupyter Server permissions. This issue is fixed in version 2.21.0.
Source: the CVE record as published by its numbering authority, via NVD and CVE.org.
The underlying weakness: Insertion of Sensitive Information into Log File
The product writes sensitive information to a log file.
How developers prevent this class of flaw
- Consider seriously the sensitivity of the information written into log files. Do not write secrets into the log files.
- Remove debug log files before deploying the application into production.
- Protect log files against unauthorized read/write.
More Insertion of Sensitive Information into Log File vulnerabilities (CWE-532)
Timeline
- CVE record published.
- CISA published its SSVC assessment (exploitation: none, automatable: no, technical impact: total).
- Record last changed materially (score, affected products, status or references).
References
Patches and release notes
Other vulnerabilities in jupyter_server
- 8.8 High severity
- 7.3 High severity
- 8.8 High severity
- 7.5 High severity
- 8.8 High severity
- 7.5 High severity
Recent Insertion of Sensitive Information into Log File vulnerabilities
- 8.8 High severity
- 7.5 High severity
- 7.7 High severity
- 7.7 High severity
- 8.8 High severity
- 7.5 High severity
Spotted an error? Tell us.