python-zeroconf
CVE-2026-48487
MEDIUM
GHSA-qc2x-6f54-m6h9
Severity by source
AV:A/AC:L/PR:N/UI:N/S:U/C:N/I:H/A:N
Adjacent multicast vector with no authentication or user interaction; I:H reflects full cache poisoning; no confidentiality or availability impact confirmed.
Primary rating from GitHub Advisory.
CVSS VectorGitHub Advisory
CVSS:3.1/AV:A/AC:L/PR:N/UI:N/S:U/C:N/I:H/A:N
Lifecycle Timeline
2Blast Radius
ecosystem impact- 6 pypi packages depend on zeroconf (3 direct, 3 indirect)
Ecosystem-wide dependent count for version 0.149.16.
DescriptionGitHub Advisory
Impact
_read_character_string and _read_string in src/zeroconf/_protocol/incoming.py sliced self.data[self.offset : self.offset + length] and advanced self.offset by the declared length without checking it against self._data_len. Python's slice silently returns fewer bytes when the end index runs past the buffer, so a record whose 16-bit RDLENGTH (RFC 1035 §3.2.1) over-advertised by tens of kilobytes was constructed from a truncated payload, appended to DNSIncoming._answers, and committed to the cache before any later parse failure surfaced. The follow-up _read_name for the next record then failed, but the corrupt record had already entered the answer list and propagated to DNSCache and ServiceInfo.
Any unauthenticated host on the local link (UDP/5353, 224.0.0.251 / ff02::fb) can multicast a single mDNS response carrying a TXT, HINFO, or A/AAAA record that advertises rdlength=65535 and only a handful of real payload bytes; consumers calling ServiceInfo.properties then parse the truncated bytes as if they matched the wire, and downstream integrations (Home Assistant and other zeroconf-driven discovery) trust the decoded record. The bug is parser-state desync rather than RCE, but it seeds the cache with attacker-shaped key/value and address records for a TTL window and is a building block for higher-impact chains.
The impact is likely lower than the other recently released advisories as there is no additional risk of OOM so the severity was manually set to low to override the score CVSS:3.1/AV:A/AC:L/PR:N/UI:N/S:U/C:N/I:H/A:N (6.5, Medium) since that doesn't fully consider the mDNS threat model.
Patches
Fixed in zeroconf 0.149.16 (PR #1756). Note that this change originally intended to ship in 0.149.13 but we ran out of space on PyPI: see https://github.com/python-zeroconf/python-zeroconf/issues/1769
Upgrade to >= 0.149.16.
Workarounds
There is no in-process workaround; upgrading is the fix. Otherwise, restrict mDNS (UDP/5353) to trusted Layer-2 segments via AP client isolation, guest-network separation, or host firewall rules.
Resources
- PR #1756, fix
- Issue #1752, public tracking issue
- RFC 1035 §3.2.1, RFC 1035 §3.3, CWE-130
AnalysisAI
Cache poisoning in python-zeroconf before 0.149.16 allows any unauthenticated adjacent-network attacker to inject attacker-controlled DNS records into the local mDNS cache by multicasting a single crafted UDP packet on port 5353. The parser in _read_character_string and _read_string advanced its offset by a caller-declared length without validating it against the actual packet buffer size; Python's silent slice truncation meant over-advertised records were accepted and committed to DNSCache and ServiceInfo intact. …
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Attack ChainAIDerived
Hypothetical attack flow derived from CVE metadata
Vulnerability AssessmentAI
| Exploitation | Exploitation requires the attacker to be on the same Layer-2 network segment as the target (or able to deliver UDP multicast to 224.0.0.251 or ff02::fb on port 5353 via multicast routing-uncommon in typical deployments). … Additional conditions and limiting factors are described in the full assessment. |
| Risk Assessment | The NVD/vendor CVSS 3.1 base score of 6.5 (AV:A/AC:L/PR:N/UI:N/S:U/C:N/I:H/A:N) is mechanically correct but the vendor explicitly overrode the severity rating to 'low', arguing the mDNS threat model limits exploitability and impact. … Full risk analysis with EPSS, KEV, and SSVC signal comparison available after sign-in. |
| Exploit Scenario | An attacker connected to the same Wi-Fi or LAN segment sends a single crafted mDNS UDP response to multicast 224.0.0.251:5353, carrying a TXT record with rdlength set to 65535 and only a handful of real payload bytes. The zeroconf parser accepts the truncated record without error and commits it to DNSCache, injecting attacker-chosen key/value pairs under a legitimate-looking service name for the duration of the TTL window. … |
| Remediation | Upgrade python-zeroconf to version 0.149.16 or later; this is the only code-level fix and no in-process workaround exists. … Detailed patch versions, workarounds, and compensating controls in full report. |
Threat intelligence, references, and detailed analysis are available after sign-in.
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Same technique Information Disclosure
View allVendor StatusVendor
SUSE
Severity: Moderate| Product | Status |
|---|---|
| SUSE Package Hub 15 SP7 | Fixed |
| openSUSE Tumbleweed | Fixed |
| SUSE Package Hub 15 SP7 | Affected |
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