PatchTheCVECVE-2020-15166: In ZeroMQ before version 4.3.3, there is a denial-of-service vulnerability
CVE-2020-15166 is a high-severity flaw (CVSS 7.5) affecting libzmq, fedora, debian linux. Below: why it ranks where it does, which versions are affected, what to do, and the exact commands.
In ZeroMQ before version 4.3.3, there is a denial-of-service vulnerability. Users with TCP transport public endpoints, even with CURVE/ZAP enabled, are impacted. If a raw TCP socket is opened and connected to an endpoint that is fully configured with CURVE/ZAP, legitimate clients will not be able to exchange any message. Handshakes complete successfully, and messages are delivered to the library, but the server application never receives them. Th
Why this priority
- High severity
- Remotely exploitable, no login, no user action
- On your watchlist
A fixed release or distro patch exists.
Risk facts
| CVSS score | 7.5 (High) |
| Attack vector | Network (remote) |
| Attack complexity | Low |
| Privileges needed | None |
| User interaction | None |
| EPSS exploit chance | 3.3% (top 11%) |
| CISA exploited list | No |
| Weakness | CWE-400 |
| Published | 2020-09-11 |
| Last modified | 2026-06-17 |
Last updated 2026-06-17 · Sources: CVE Program, NVD, CISA KEV, EPSS and vendor advisories · How we score
Am I affected?
Timeline
- Published CVE record published
- Updated Record last modified
Scores and fixes here are computed automatically from those and other public sources. Confirm with the vendor advisory before changing production systems.
Quick answers
How do I fix CVE-2020-15166?
libzmq: upgrade to 4.3.3; fedora: mitigate or apply the listed mitigation; debian linux: mitigate or apply the listed mitigation. Exact commands for each OS are on this page.
Is CVE-2020-15166 being exploited?
CVE-2020-15166 is not on the CISA Known Exploited Vulnerabilities list at the time of the last update. Check again, as this can change.
What does CVE-2020-15166 affect?
CVE-2020-15166 affects libzmq, fedora, debian linux. Severity is high (CVSS 7.5). In ZeroMQ before version 4.3.3, there is a denial-of-service vulnerability. Users with TCP transport public endpoints, even with CURVE/ZAP enabled, are impacted. If a raw TCP socket is opened and connected to an endpoint that is fully confi
How urgent is CVE-2020-15166?
Priority 58/100. High severity; Remotely exploitable, no login, no user action; On your watchlist
Software pages
Related CVEs
- CVE-2021-20237 HIGH 7.5 UPGRADE An uncontrolled resource consumption (memory leak) flaw was found in ZeroMQ's src/xpub.cpp in versions before
- CVE-2021-20235 HIGH 8.1 UPGRADE There's a flaw in the zeromq server in versions before 4.3.3 in src/decoder_allocators.hpp
- CVE-2021-20234 MEDIUM 6.5 UPGRADE An uncontrolled resource consumption (memory leak) flaw was found in the ZeroMQ client in versions before 4.3.
- CVE-2020-36400 CRITICAL 9.8 DOWNGRADE ZeroMQ libzmq 4.3.3 has a heap-based buffer overflow in zmq::tcp_read, a different vulnerability than CVE-2021
- CVE-2019-6250 HIGH 8.8 UPGRADE MITIGATE A pointer overflow, with code execution, was discovered in ZeroMQ libzmq (aka 0MQ) 4.2.x and 4.3.x before 4.3.