# CVE-2026-48487: python-zeroconf cache poisoning via unvalidated RDLENGTH

Source: https://junglewise.ai/threats/cve-2026-48487-python-zeroconf-cache-poisoning-via-unvalidated-rdlength  
Publisher: Junglewise Threat Intelligence, https://junglewise.ai/threats  
Published: 2026-07-17. Updated: 2026-07-17  
License: CC BY 4.0 with a link back

CVE-2026-48487 · Severity: medium · CVSS 6.5 · Published 2026-07-17

Zeroconf is a Python library used by smart home software and other applications to automatically discover devices on a local network. A flaw in how it handles network messages allows an attacker on the same local network to send specially crafted data that corrupts the library's internal cache. This could lead to applications receiving incorrect information about available devices or services, potentially disrupting operations or facilitating further attacks.

Technologies: [zeroconf (PyPI)](https://junglewise.ai/threats/technologies/zeroconf), [Python-Zeroconf](https://junglewise.ai/threats/technologies/python-zeroconf). Vendors: [PyPI](https://junglewise.ai/threats/vendors/pypi), [Python-Zeroconf](https://junglewise.ai/threats/vendors/python-zeroconf).

## Quick answers

**Is CVE-2026-48487 exploited in the wild?** No. Junglewise Threat Intelligence has no report of CVE-2026-48487 being exploited in the wild.

**How severe is CVE-2026-48487?** Medium severity, with a CVSS score of 6.5, published 17 July 2026.

**Which products and versions are affected?** zeroconf (PyPI) < 0.149.16, ECOSYSTEM:introduced=0,fixed=0.149.16; Python-Zeroconf < 0.149.16.

**Is there a fix for CVE-2026-48487?** Yes. zeroconf (PyPI): upgrade to 0.149.16 or later. Junglewise finds every place you run it, drafts the upgrade and applies it once you approve.

**How is CVE-2026-48487 attacked?** It is attacked from the adjacent network, in a software library.

**Am I affected by CVE-2026-48487?** Check whether you run zeroconf (PyPI) or Python-Zeroconf at an affected version. Junglewise does that check for you around the clock: connect your code, cloud and domains, and it matches new vulnerabilities like this one against what you actually run and tells you when one reaches you.

## How to fix

- zeroconf (PyPI): upgrade to 0.149.16 or later

  ```sh
  pip install "zeroconf>=0.149.16"
  ```


## Technical details

A vulnerability exists in the `_read_character_string` and `_read_string` functions within `src/zeroconf/_protocol/incoming.py`. The parser advances the internal data offset by an attacker-declared `RDLENGTH` without verifying it against the actual remaining buffer length (`self._data_len`). Because Python's slicing mechanism silently returns fewer bytes when an index exceeds the buffer, the library constructs and caches truncated TXT, HINFO, or A/AAAA records before a subsequent parse error occurs. This allows unauthenticated adjacent attackers to perform cache poisoning and parser-state desynchronization. The issue is addressed in version 0.149.16 by implementing explicit bounds checks.

## Affected products

- python-zeroconf zeroconf < 0.149.16

## Identifiers

- CVE-2026-48487
- GHSA-qc2x-6f54-m6h9
- PYSEC-2026-3438

## Timeline

- 2026-05-20: patched: Fix merged in PR #1756
- 2026-05-21: advisory: GHSA-qc2x-6f54-m6h9 published
- 2026-07-17: disclosed: CVE-2026-48487 published to NVD

## References

- [https://github.com/python-zeroconf/python-zeroconf/commit/544449596e645fcaad3834fa0cb614a54f847a82](https://github.com/python-zeroconf/python-zeroconf/commit/544449596e645fcaad3834fa0cb614a54f847a82)
- [https://github.com/python-zeroconf/python-zeroconf/issues/1752](https://github.com/python-zeroconf/python-zeroconf/issues/1752)
- [https://github.com/python-zeroconf/python-zeroconf/pull/1756](https://github.com/python-zeroconf/python-zeroconf/pull/1756)
- [https://github.com/python-zeroconf/python-zeroconf/releases/tag/0.149.16](https://github.com/python-zeroconf/python-zeroconf/releases/tag/0.149.16)
- [https://github.com/python-zeroconf/python-zeroconf/security/advisories/GHSA-qc2x-6f54-m6h9](https://github.com/python-zeroconf/python-zeroconf/security/advisories/GHSA-qc2x-6f54-m6h9)

## Related threats

- [python-zeroconf denial of service via unbounded TC-deferred queue](https://junglewise.ai/threats/cve-2026-48045-python-zeroconf-denial-of-service-via-unbounded-tc-deferred-queue)
- [python-zeroconf memory exhaustion via unbounded DNS cache](https://junglewise.ai/threats/cve-2026-47184-python-zeroconf-memory-exhaustion-via-unbounded-dns-cache)
- [python-zeroconf memory exhaustion via malformed mDNS packets](https://junglewise.ai/threats/cve-2026-47183-python-zeroconf-memory-exhaustion-via-malformed-mdns-packets)
- [python-zeroconf uncontrolled recursion in DNS compression-pointer decoder](https://junglewise.ai/threats/cve-2026-47180-python-zeroconf-uncontrolled-recursion-in-dns-compression-pointer)