medium CVSS 6.5

CVE-2026-47183·Python vulnerability

Zeroconf is a pure Python implementation of multicast DNS service discovery. Prior to 0.149.6, DNSIncoming._log_exception_debug and the four QuietLogger exception-dedup methods stored an unbounded _seen_logs dictionary keyed by attacker-influenced IncomingDecodeError messages, retaining sys.exc_info() tracebacks whose frame locals kept raw packet self.data buffers and allowing unauthenticated hosts on the local link over UDP/5353 (224.0.0.251 / ff02::fb) to drive memory growth until mDNS-dependent features degrade or the process is OOM-killed. This issue is fixed in version 0.149.6.

Severity
medium
Software
Python
Fixed in
0.149.6
Published
2026-07-17

Affected versions

Until: 0.149.6

Fixed in: 0.149.6

How to fix this CVE

Update the Python Zeroconf library to version 0.149.6 or later to fix a memory exhaustion vulnerability in the mDNS service discovery implementation. This vulnerability allows unauthenticated local network attackers to trigger unbounded memory growth by sending specially crafted multicast DNS packets, potentially causing application degradation or process termination. Affected systems running Zeroconf-dependent services should prioritize this update immediately.

sudo dnf update python3-zeroconf

Defensia detects this vulnerability

How to check if you are affected

  1. Step 1: Check the installed Zeroconf version with: pip3 show zeroconf | grep Version
  2. Step 2: Verify if mDNS services are active by checking for listening processes on port 5353: sudo netstat -tlnup | grep 5353 or sudo ss -tlnup | grep 5353
  3. Step 3: Monitor system memory usage during normal operation and look for unexplained growth patterns, especially if the system is on a shared local network: free -h && watch -n 1 free -h
  4. Step 4: After upgrading, re-run pip3 show zeroconf to confirm the version is 0.149.6 or higher

FAQ

What is CVE-2026-47183?

This vulnerability is a memory exhaustion flaw in Python Zeroconf's mDNS implementation where the library stores unbounded exception logs keyed by attacker-controlled error messages, allowing local network attackers to exhaust system memory and degrade or crash mDNS-dependent services.

Is CVE-2026-47183 being actively exploited?

No, this vulnerability is not currently listed on the CISA Known Exploited Vulnerabilities (KEV) catalog, and no public exploits are available. However, it remains a valid denial-of-service concern for systems on untrusted local networks.

What versions of Python Zeroconf are affected by CVE-2026-47183?

All versions of python-zeroconf prior to 0.149.6 are vulnerable. The fix is included starting with version 0.149.6.

How do I check if my server is vulnerable to CVE-2026-47183?

Run pip3 show zeroconf and check the Version field. If the version is below 0.149.6, your system is vulnerable.

Does Defensia detect CVE-2026-47183?

Yes — Defensia's CVE advisory scanner compares installed package versions against the NVD database. If Python Zeroconf is installed on a monitored server, CVE-2026-47183 will appear in your dashboard with remediation steps.

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References

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