CVE-2020-25686
Publication date 19 January 2021
Last updated 11 August 2025
Ubuntu priority
Description
A flaw was found in dnsmasq before version 2.83. When receiving a query, dnsmasq does not check for an existing pending request for the same name and forwards a new request. By default, a maximum of 150 pending queries can be sent to upstream servers, so there can be at most 150 queries for the same name. This flaw allows an off-path attacker on the network to substantially reduce the number of attempts that it would have to perform to forge a reply and have it accepted by dnsmasq. This issue is mentioned in the "Birthday Attacks" section of RFC5452. If chained with CVE-2020-25684, the attack complexity of a successful attack is reduced. The highest threat from this vulnerability is to data integrity.
Status
| Package | Ubuntu Release | Status |
|---|---|---|
| dnsmasq | 25.04 plucky |
Fixed 2.82-1ubuntu2
|
| 24.04 LTS noble |
Fixed 2.82-1ubuntu2
|
|
| 22.04 LTS jammy |
Fixed 2.82-1ubuntu2
|
|
| 20.04 LTS focal |
Fixed 2.80-1.1ubuntu1.2
|
|
| 18.04 LTS bionic |
Fixed 2.79-1ubuntu0.2
|
|
| 16.04 LTS xenial |
Fixed 2.75-1ubuntu0.16.04.7
|
|
| 14.04 LTS trusty | Ignored changes too intrusive |
Severity score breakdown
| Parameter | Value |
|---|---|
| Base score |
3.7 · Low
|
| Attack vector | Network |
| Attack complexity | High |
| Privileges required | None |
| User interaction | None |
| Scope | Unchanged |
| Confidentiality | None |
| Integrity impact | Low |
| Availability impact | None |
| Vector | CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:N/I:L/A:N |
References
Related Ubuntu Security Notices (USN)
- USN-4698-1
- Dnsmasq vulnerabilities
- 19 January 2021