How severe is CVE-2026-25518?

CVE-2026-25518 has a CVSS score of 5.9/10, rated MEDIUM. Review your exposure and patch according to your risk tolerance.

Which packages are affected by CVE-2026-25518?

CVE-2026-25518 affects the following packages: github.com/cert-manager/cert-manager (Go), github.com/cert-manager/cert-manager (Go). Ecosystems affected: Go.

How do I fix CVE-2026-25518?

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.

How do I detect CVE-2026-25518 in my Go dependencies?

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.

How do I mitigate CVE-2026-25518 if there is no patch (or I can't update yet)?

Cap what an attacker can consume: apply request size, rate and timeout limits in front of the affected component, and run it with memory and CPU limits so exhaustion degrades one worker rather than the whole service.

Is CVE-2026-25518 actively exploited in the wild?

No public exploit code has been indexed for CVE-2026-25518 yet. This does not mean the vulnerability cannot be exploited — absence of public exploits does not imply safety. Apply the recommended fix and use O3 Security to monitor your exposure.

What is the EPSS score for CVE-2026-25518?

CVE-2026-25518 has an EPSS (Exploit Prediction Scoring System) score of 0.4%, placing it in the 31th percentile of all CVEs. EPSS is maintained by FIRST.org and estimates the probability that a vulnerability will be exploited in the wild within the next 30 days. This score indicates relatively lower exploitation probability, though the CVSS severity should still guide your patching priority.

What type of vulnerability is CVE-2026-25518?

CVE-2026-25518 is classified as CWE-129 (CWE-129), CWE-704 (CWE-704). These weakness types describe the underlying flaw category, which helps determine the potential impact and the right class of mitigation.

When was CVE-2026-25518 published, and has it been updated?

CVE-2026-25518 was published on February 4, 2026 and was last updated on October 28, 2026. Advisory data evolves as severity scores, affected ranges, and exploit intelligence are revised — always check the latest version of the advisory before acting.

🐹

🐹 Go

Not in CISA KEV

MEDIUM severity

CVE-2026-25518 — cert-manager

MEDIUMFix: cert-manager/cert-manager@409fc24

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

Also known asBIT-cert-manager-2026-25518GHSA-gx3x-vq4p-mhhvGO-2026-4399

Published

Feb 4, 2026

Updated

Oct 28, 2026

Affected

2 pkgs

Patched

2 / 2

Exploits

None indexed

Exploitation data as of Nov 8, 2026 · OSV.dev, NVD, FIRST.org (EPSS)

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

via FIRST.org ↗

0.4%probability of exploitation in next 30 days

Lower Risk-0.00%

Lower risk than most CVEs31th percentile — riskier than 31% of all scored CVEsHighest risk

Probability of exploitation in the next 30 days, from FIRST.org EPSS.

How urgent is this, really

Where this sits among everything scored

Real-World Exposure

2 pkgs affected

🐹github.com/cert-manager/cert-manager🐹github.com/cert-manager/cert-manager

Real-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

2 total 2 fixed

Ecosystem	Package	Vulnerable range	Fix
🐹Go	`github.com/cert-manager/cert-manager`	≥ 1.18.0&&< 1.18.5	1.18.5`go get github.com/cert-manager/cert-manager@v1.18.5`
🐹Go	`github.com/cert-manager/cert-manager`	≥ 1.19.0&&< 1.19.3	1.19.3`go get github.com/cert-manager/cert-manager@v1.19.3`

Affected Products

1 product · 2 configurations

Application

cert-managercert-manager

≥ 1.19.0 && < 1.19.3

range

Detection & mitigation playbook

Open-source dependency

Detect
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
Cap what an attacker can consume: apply request size, rate and timeout limits in front of the affected component, and run it with memory and CPU limits so exhaustion degrades one worker rather than the whole service.

Fixing This On Your OS

If you run this on a Linux distribution, patch through your package manager against the distro's own security advisory below — it tracks the exact backported fix for your release, which can ship on a different timeline (and sometimes a different severity) than the upstream project.

Red HatModerate

Workaround published by Red Hat

Mitigation for this issue is either not available or the currently available options do not meet the Red Hat Product Security criteria comprising ease of use and deployment, applicability to widespread installation base or stability.

Source: Red Hat security advisory for CVE-2026-25518 (CC BY 4.0)

Frequently Asked Questions

### 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. ### Patch