CVE-2025-5994
Cache poisoning via the ECS-enabled Rebirthday Attack
No known exploitation. EPSS puts it in the 9th percentile. A vendor fix is available.
What to do
The vendor has published a fix. Version details are below where the sources state them.
What it is
From the CVE record
A multi-vendor cache poisoning vulnerability named 'Rebirthday Attack' has been discovered in caching resolvers that support EDNS Client Subnet (ECS). Unbound is also vulnerable when compiled with ECS support, i.e., '--enable-subnet', AND configured to send ECS information along with queries to upstream name servers, i.e., at least one of the 'send-client-subnet', 'client-subnet-zone' or 'client-subnet-always-forward' options is used. Resolvers supporting ECS need to segregate outgoing queries to accommodate for different outgoing ECS information. This re-opens up resolvers to a birthday paradox attack (Rebirthday Attack) that tries to match the DNS transaction ID in order to cache non-ECS poisonous replies.
In plain language
No plain-language summary for this CVE yet.
Exploitation
Where each signal puts this CVE on the scale from published to confirmed exploited.
- CISA KEV
Not in the catalog. CISA has not confirmed exploitation.
- Public exploits
No public exploit or proof of concept found in the sources we track.
- EPSS
0.2% chance of exploitation activity in the next 30 days, which ranks it in the 9th percentile of scored CVEs.
Exploit Prediction Scoring System, FIRST.org. A probability, not a confirmation.
Lifecycle
5 events over 344 days, from the signal feeds we watch.
- OpenVAS check added
- Patch availablerecord updated
- Publishedweakness classified
Affected products
And 2 more affected products. See all after sign-in
Technical detail
CVSS 3.1 vector
Open in the CVSS calculatorAV:N/AC:L/PR:N/UI:N/S:U/C:N/I:H/A:N
Scored 7.5 by bdu.
How it is reached
- Access Vector NetworkExploitable remotely over the network
- Access Complexity LowNo special conditions required
Impact if exploited
- Confidentiality NoneNo confidentiality impact
- Integrity H
- Availability NoneNo availability impact
Weaknesses
Sources
References in the record
- nlnetlabs.nl/downloads/unbound/CVE-2025-5994.txt
- lists.debian.org/debian-lts-announce/2025/08/msg00019.html
- nlnetlabs.nl/downloads/unbound/CVE-2025-5994.txt&
And 8 more references. See all after sign-in
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