CVE-2026-25518 is a medium-severity (CVSS 5.9) CWE-129 vulnerability in github.com/cert-manager/cert-manager. A fix is available for github.com/cert-manager/cert-manager — see the affected versions and patch details below.
cert-manager-controller DoS via Specially Crafted DNS Response
Exploitation Status
No confirmed exploitation observed yet
- CISA’s own triage has not observed active exploitation or public proof-of-concept code for this CVE as of its last assessment.
Exploitation and automatability from CISA’s SSVC triage for CVE-2026-25518.
EPSS Exploitation Probability
EPSS (Exploit Prediction Scoring System) is a daily probability model maintained by FIRST.org. It estimates the likelihood a CVE will be exploited in production environments within the next 30 days, derived from real-world threat intelligence signals.
How urgent is this, really
CVE-2026-25518 plotted by exploitation likelihood (EPSS) against impact (CVSS). The shaded corner — EPSS 50%+ and CVSS 7.0+ — is where this CVE doesn't sit, though severity or exploitability alone can still warrant action.
Where this sits among everything scored
Of 378,156 CVEs with a current EPSS score, this one falls in the < 10% band (highlighted). Real counts from FIRST.org, not a sample — log-scaled since the landscape is heavily right-skewed.
Real-World Exposure
github.com/cert-manager/cert-manager🐹github.com/cert-manager/cert-managerReal-time download stats are indexed for npm and PyPI packages. This vulnerability affects Go packages — download data is not available via public APIs for these ecosystems.
Description
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!
Affected Packages
| Ecosystem | Package | Vulnerable range | Fix |
|---|---|---|---|
| 🐹Go | github.com/cert-manager/cert-manager | ≥ 1.18.0&&< 1.18.5 | 1.18.5go get github.com/cert-manager/cert-manager@v1.18.5 |
| 🐹Go | github.com/cert-manager/cert-manager | ≥ 1.19.0&&< 1.19.3 | 1.19.3go get github.com/cert-manager/cert-manager@v1.19.3 |
Detection & mitigation playbook
Open-source dependencyDetect
Scan your dependency tree (package-lock.json, pnpm-lock.yaml, requirements.txt, go.sum, etc.) for github.com/cert-manager/cert-manager, including transitive dependencies — a direct dependency you never call can still pull in a vulnerable version.
Fix
Update github.com/cert-manager/cert-manager to 1.18.5 or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms CVE-2026-25518 is resolved across your whole dependency graph.
Workarounds
If you can't upgrade right away: gate or disable the affected feature, validate untrusted input at the boundary, and avoid passing attacker-controlled data into the vulnerable path. O3's runtime protection blocks exploitation in production as an interim safeguard until the upgrade lands.
How O3 protects you
O3 Security's impact-aware SCA analyses which vulnerable code paths your application actually calls, so a match like CVE-2026-25518 can be triaged on real exposure rather than presence alone.
Tailored to CVE-2026-25518. Runtime protection reduces exposure until a permanent patch is applied and verified — it complements patching, it doesn't replace it.
Frequently Asked Questions
Is CVE-2026-25518 in your dependencies?
O3 Security finds CVE-2026-25518 across Go dependencies, including transitive ones, and its impact-aware SCA ranks findings by whether your code actually calls the vulnerable path.