Possible cache poisoning vulnerability via a cache side-channel exposed by 'unwanted-reply-threshold'
CVSS score
5.3
EPSS probability
—
Risk score
0.5
Published
2 h ago
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Vulnerability description
DayBreach AI Explanation
Verified against sourcesSources read
1
Source agreement
Tam uyum
Evidence confidence
%55
Short explanation
A cache side-channel vulnerability exists in NLnet Labs Unbound due to the unwanted-reply-threshold configuration. This can lead to source port probing followed by cache poisoning via TXID guessing.
This vulnerability allows attackers to observe cache clearing behavior to determine the upstream source port and subsequently perform cache poisoning.
What should be done?
- Follow vendor advisories
- Review unwanted-reply-threshold configuration
Chain of evidence and sources
NLnet Labs Unbound 1.26.1 ve önceki sürümleri, unwanted-reply-threshold yapılandırması üzerinden bir önbellek yan kanalı barındırmaktadır.
Önbellek temizleme eylemi mevcut upstream UDP bekleyen sorgusunu yok etmez, bu da harici bir gözlemcinin kaynak portunu test etmesini sağlar.
Show the technical text from the sources
In NLnet Labs Unbound up to and including version 1.26.1, an observable cache-level side-channel can be exposed with 'unwanted-reply-threshold > 0' configurations (not a default configuration). If a response-like UDP datagram reaches the upstream source port currently used by a recursive query, but its TXID does not match any pending query, Unbound counts the packet as an unwanted reply. When the accumulated count reaches the configured threshold, Unbound clears the worker's RRset cache and message cache. This cache clear action does not destroy the current upstream UDP pending query. Therefore, an external observer can distinguish whether a candidate port matches the current upstream source port by checking whether an existing cached item has been cleared. This is a cache side-channel vulnerability that can be used to probe the upstream source port. Although the attack is not feasible on default configurations and the suggested value (10 million) makes it an ureliable attack on a public resolver, in scenarios where the attacker can keep a concurrent query window alive, the attacker can first filter the source port and then perform birthday-style guessing against the TXID, making cache poisoning a feasible attack path.
CVSS vector: CVSS:3.1/AV:A/AC:H/PR:N/UI:N/S:U/C:N/I:H/A:N
CWE: CWE-205
This explanation was compiled automatically from the source records. Scores, active exploitation, patch and exploit status come straight from the sources.
IMPACT: Affected Products and Software
Affected Products
The following products are affected by CVE-2026-109125 vulnerability. Where our threat engine knows the exact affected versions, they are listed below.
| ID | VENDOR | PRODUCT | ACTION |
|---|---|---|---|
| 1 | NLnet Labs | Unbound | View |
RED HAT CSAF/VEX: Product Impact Check
SCORING: CVSS from Multiple Sources
CVSS Scores
The Common Vulnerability Scoring System is a standardised framework for assessing the severity of vulnerabilities in software and systems. We collect and display CVSS scores from several sources for each CVE.
| SCORE | VERSION | SEVERITY | VECTOR | SOURCE |
|---|---|---|---|---|
| 5.3 | CVSS V3_1 | MEDIUM | CVSS:3.1/AV:A/AC:H/PR:N/UI:N/S:U/C:N/I:H/A:N | CVE CNA |
| 5.3 | CVSS V31 | MEDIUM | CVSS:3.1/AV:A/AC:H/PR:N/UI:N/S:U/C:N/I:H/A:N | NVD |
Patch and Remediation Guide
Solution & Remediation Advisory
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Public exploit and active exploitation status
Verified exploit intelligence
No verified public PoC, exploit repository or Metasploit module has been found for this CVE yet.
Weakness Classification and Attack Patterns (CWE & CAPEC)
CWE - Common Weakness Enumeration
While CVE identifies specific instances of vulnerabilities, CWE categorises the common flaws or weaknesses that can lead to vulnerabilities. CVE-2026-109125 is associated with the following CWEs:
Common Attack Pattern Enumeration and Classification (CAPEC)
Common Attack Pattern Enumeration and Classification (CAPEC) stores attack patterns, which are descriptions of the common attributes and approaches employed by adversaries to exploit the CVE-2026-109125 weaknesses.
Attack Vector and Accessibility
Official Sources and Advisories
CVSS Vector Radar Chart
5.3 / 10Vulnerability Scoring Details
CVSS:3.1/AV:A/AC:H/PR:N/UI:N/S:U/C:N/I:H/A:NYama durumu bilinmiyor
Weakness Type (CWE & CAPEC)
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