CVE-2026-25518: cert-manager-controller DoS via Specially Crafted DNS Response
Impact
The cert-manager-controller performs DNS lookups during ACME DNS-01 processing (for zone discovery and propagation self-checks). By default, these lookups use standard unencrypted DNS.
An attacker who can intercept and modify DNS traffic from the cert-manager-controller pod can insert a crafted entry into cert-manager's DNS cache. Accessing this entry will trigger a panic, resulting in Denial of Service (DoS) of the cert-manager controller.
The issue can also be exploited if the authoritative DNS server for the domain being validated is controlled by a malicious actor.
Patches
The vulnerability was introduced in cert-manager v1.18.0 and has been patched in cert-manager v1.19.3 and v1.18.5, which are the supported minor releases at the time of publishing.
cert-manager versions prior to v1.18.0 are unaffected.
Workarounds
- Using DNS-over-HTTPS reduces the risk of DNS traffic being intercepted and modified. - Note that DNS-over-HTTPS does not prevent the risk of an attacker-controlled authoritative DNS server.
Resources
- Fix for cert-manager 1.18: https://github.com/cert-manager/cert-manager/pull/8467 - Fix for cert-manager 1.19: https://github.com/cert-manager/cert-manager/pull/8468 - Fix for master branch: https://github.com/cert-manager/cert-manager/pull/8469
Credits
Huge thanks to Oleh Konko (@1seal) for reporting the issue, providing a detailed PoC and an initial patch!
Other sources
cert-manager adds certificates and certificate issuers as resource types in Kubernetes clusters, and simplifies the process of obtaining, renewing and using those certificates. In versions from 1.18.0 to before 1.18.5 and from 1.19.0 to before 1.19.3, the cert-manager-controller performs DNS lookups during ACME DNS-01 processing (for zone discovery and propagation self-checks). By default, these lookups use standard unencrypted DNS. An attacker who can intercept and modify DNS traffic from the cert-manager-controller pod can insert a crafted entry into cert-manager's DNS cache. Accessing this entry will trigger a panic, resulting in denial‑of‑service (DoS) of the cert-manager controller. The issue can also be exploited if the authoritative DNS server for the domain being validated is controlled by a malicious actor. This issue has been patched in versions 1.18.5 and 1.19.3.
— MITRE
Affected Software
Remediation
Patch Available
Patch Available
Patch Available
Event History
Frequently Asked Questions
What is the severity of CVE-2026-25518?
CVE-2026-25518 is classified as a DoS vulnerability in the cert-manager-controller.
How do I fix CVE-2026-25518?
To fix CVE-2026-25518, upgrade cert-manager to version 1.19.3 or 1.18.5 or later.
What versions are affected by CVE-2026-25518?
CVE-2026-25518 affects cert-manager versions between 1.18.0 and 1.18.5 and 1.19.0 and 1.19.3.
What is the impact of CVE-2026-25518?
The impact of CVE-2026-25518 is a potential denial of service due to specially crafted DNS responses.
Who can exploit CVE-2026-25518?
An attacker with the ability to intercept and modify DNS responses can exploit CVE-2026-25518.