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Mallory
Medium

Unbound cache poisoning via promiscuous NS RRSets

IdentifiersCVE-2025-11411CWE-345

NLnet Labs Unbound, a validating recursive caching DNS resolver, is vulnerable to cache poisoning and possible domain hijack attacks in versions up to and including 1.24.1 due to incorrect handling of unsolicited or promiscuous NS RRSets included in DNS replies. NS records placed in the authority section can be accepted with sufficient trust and used to update cached delegation information for a zone, even when those records are not legitimately solicited for that response context. An attacker able to inject such NS RRSets, and potentially corresponding address records, into a DNS reply can cause Unbound to replace or augment its cached delegation data for the affected delegation point. The issue is exploitable through forged or spoofed packets and fragmentation-based injection scenarios. Version 1.24.1 introduced a partial fix that scrubs unsolicited NS RRSets and related address records from replies, but additional cases involving YXDOMAIN and non-referral nodata replies required a further fix in 1.24.2. Later content also notes a complementary hardening change in 1.25.1 to disregard unrelated additional-section address records.

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ANALYST BRIEF

Impact, mitigation & remediation

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Impact

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Successful exploitation allows poisoning of Unbound's DNS cache for a delegation point, enabling domain hijacking or redirection of subsequent DNS lookups to attacker-controlled name servers or infrastructure. This can facilitate man-in-the-middle conditions, traffic redirection, delivery of malicious content, interception of user connections, and disruption of normal DNS resolution. On systems using local-unbound or Unbound as a recursive resolver, the compromise affects downstream clients that rely on the poisoned cache.

Mitigation

If you can’t patch tonight, do this now.

No complete workaround is described in the provided content. Recommended mitigation is to apply the vendor security update. If Unbound or local-unbound is not required, disable the service. Administrators can also monitor DNS activity for signs of cache poisoning and ensure DNSSEC validation is enabled where applicable, though the content does not present DNSSEC as a full substitute for patching.

Remediation

Patch, then assume compromise.

Upgrade Unbound to a fixed release. The provided content states that Unbound 1.24.2 fully addresses CVE-2025-11411 by extending scrubbing of unsolicited NS RRSets and their associated address records to YXDOMAIN and non-referral nodata replies. Content also notes that Unbound 1.25.1 contains a complementary fix that disregards additional-section address records unless explicitly relevant to authority NS records. Distribution-specific guidance includes applying vendor security updates such as Debian's fixed package versions and FreeBSD patches where local-unbound is shipped. After updating, restart the Unbound/local_unbound service to ensure the patched resolver is running.
PUBLIC EXPLOITS

Exploits

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VALID 0 / 0 TOTALView more in app

No public exploit code observed for this vulnerability.

EXPOSURE SURFACE

Affected products & vendors

Products and vendors Mallory has correlated with this vulnerability. Open in Mallory to drill down to specific CPE configurations and version ranges.

VendorProductType
FreebsdFreebsdapplication
Nlnet LabsUnboundapplication
Rocky LinuxRocky Linuxoperating_system
UnboundUnboundapplication

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ACTIVITY FEED

Recent activity

21 sources tracked across advisories, community write-ups, and news. New activity surfaces here as Mallory finds it.

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Threat actor evidence

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Associated malware

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Detection signatures

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Vendor-by-vendor mapping

Cross-references every affected SKU, including bundled OEM variants.

Social activity15

Community discussion across Reddit, Mastodon, and other social sources.