CVE-2020-25687
MediumA heap-based buffer overflow was discovered in dnsmasq when DNSSEC is enabled and before it validates the received DNS entries.
Published Jan 21, 2021 · Updated Aug 5, 2026 · Also known as ALPINE-CVE-2020-25687, DEBIAN-CVE-2020-25687, UBUNTU-CVE-2020-25687
Key Facts
Patch immediately- CVE-2020-25687 is a medium-severity vulnerability (CVSS 5.9 v3.1) affecting Dnsmasq (Thekelleys), Debian Linux, Fedora (Fedoraproject) and 1 more product.
- It is not listed in any known-exploited vulnerabilities catalog. No public exploit code is known.
- EPSS estimates a 87% probability of exploitation in the next 30 days.
- Fixed versions are available, including Dnsmasq 0:2.79-11.el8_2.2, Dnsmasq 2.75-1ubuntu0.16.04.7, Dnsmasq 2.76-5+deb9u3.
- Brandefense priority: patch immediately, because it is very likely to be exploited soon.
CVSS v3.1
5.9
CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:N/I:N/A:H
EPSS (30-day exploit likelihood)
87%
Higher than 99.7% of all scored CVEs
Exploited in the wild
No known
Not in a known-exploited catalog
Public exploit code
None known
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Description
A flaw was found in dnsmasq before version 2.83. A heap-based buffer overflow was discovered in dnsmasq when DNSSEC is enabled and before it validates the received DNS entries. This flaw allows a remote attacker, who can create valid DNS replies, to cause an overflow in a heap-allocated memory. This flaw is caused by the lack of length checks in rfc1035.c:extract_name(), which could be abused to make the code execute memcpy() with a negative size in sort_rrset() and cause a crash in dnsmasq, resulting in a denial of service. The highest threat from this vulnerability is to system availability.
Affected Products
105 affected entries in total| Product | Affected versions | Fixed in |
|---|---|---|
| DnsmasqThekelleys | >= dnsmasq 2.83 | 2.83 |
| Debian LinuxDebian | 10.0, 9.0 | n/a |
| FedoraFedoraproject | 32, 33 | n/a |
| dnsmasq-utilsoracle | See advisory | 2.79-13.el8_3.1 |
Patched Releases
Dnsmasq
0:2.79-11.el8_2.2, 2.75-1ubuntu0.16.04.7, 2.76-5+deb9u3, 2.78-0.16.14.1, 2.78-0.17.15.1, 2.78-18.15.1, 2.78-3.11.1, 2.78-7.6.1, 2.78-lp151.5.6.1, 2.78-lp152.7.3.1, 2.79-13.el8_3.1, 2.79-1ubuntu0.2, 2.80-1.1ubuntu1.2, 2.80-1+deb10u1, 2.82-1.ph1, 2.82-1.ph2, 2.82-1.ph3, 2.83-1, 2.83-r0, 2.85-1, 2.83
dnsmasq-utils
2.78-18.15.1, 2.78-lp151.5.6.1, 2.78-lp152.7.3.1, 2.79-13.el8_3.1
Timeline
Publicly disclosed
Jan 21, 2021
Last updated
Aug 5, 2026
Weakness Type
- CWE-122 Heap-based Buffer Overflow
References
- advisoryhttp://lists.thekelleys.org.uk/pipermail/dnsmasq-discuss/2021q1/014599.html
- advisoryRHSA-2021:0150
- advisoryRHSA-2021:0151
- advisoryRHSA-2021:0152
- advisoryhttps://access.redhat.com/security/vulnerabilities/RHSB-2021-001
FAQ
Common Questions.
A flaw was found in dnsmasq before version 2.83.
Affected: Dnsmasq (Thekelleys) versions >= dnsmasq 2.83; Debian Linux versions 10.0, 9.0; Fedora (Fedoraproject) versions 32, 33, among others. The full list is in the CVE brief.
It is not listed in any known-exploited vulnerabilities catalog.
No, it is not currently listed in the CISA Known Exploited Vulnerabilities catalog.
No public exploit code is known.
Fixed versions are available, including Dnsmasq 0:2.79-11.el8_2.2, Dnsmasq 2.75-1ubuntu0.16.04.7, Dnsmasq 2.76-5+deb9u3.
Brandefense priority: patch immediately, because it is very likely to be exploited soon.
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