CVE-2026-84961 is a high-severity (CVSS 7.4) CWE-295 vulnerability in undici. A fix is available for undici — see the affected versions and patch details below.
undici vulnerable to TLS certificate validation bypass via dropped connect options in BalancedPool
Exploitation Status
No confirmed exploitation observed yet
- A successful exploit gives an attacker total control of the affected component, not partial access.
- 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-2026-84961.
EPSS Exploitation Probability
Probability of exploitation in the next 30 days, from FIRST.org EPSS.
How urgent is this, really
CVE-2026-84961 by exploitation likelihood (EPSS) against impact (CVSS). Outside the shaded patch-first corner.
Where this sits among everything scored
Of 394,803 CVEs with a current EPSS score, this one falls in the < 10% band (highlighted). Counts from FIRST.org, log-scaled.
Real-World Exposure
How broadly this vulnerability is actually deployed: weekly install volume shows current usage, and reverse-dependency count shows how many other packages break if it stays unpatched.
undicinpmDescription
Impact
undici's BalancedPool passes its constructor options through a JSON-based deep clone (JSON.parse(JSON.stringify(...))) before forwarding them to each per-upstream Pool. JSON cannot represent functions, so a caller-supplied connect or tls option containing a checkServerIdentity callback (or a custom connector function) is silently dropped before it reaches the TLS layer. As a result, a TLS peer whose certificate a custom checkServerIdentity was written to reject, but which passes Node's default hostname and chain checks, is silently accepted when the request is made through BalancedPool. Client, Pool, Agent, and RoundRobinPool destructure connect/tls before the clone and are not affected. Only applications that use BalancedPool with a function-valued connect/tls option (such as a custom checkServerIdentity or connector) are affected.
Patches
Upgrade to 7.29.1 or 8.10.2. BalancedPool now preserves the connect and tls options outside the JSON clone, so custom TLS verification callbacks are forwarded to each upstream unchanged.
Workarounds
Use Client, Pool, or Agent instead of BalancedPool for connections that rely on a custom checkServerIdentity or connector, until upgraded.
Affected Packages
| Ecosystem | Package | Vulnerable range | Fix |
|---|---|---|---|
| 📦npm | undici | ≥ 7.24.1&&< 7.29.1 | 7.29.1npm install undici@7.29.1 |
| 📦npm | undici | ≥ 8.0.0&&< 8.10.2 | 8.10.2npm install undici@8.10.2 |
Affected Products
undicinodejsDetection & mitigation playbook
Open-source dependencyDetect
Scan your dependency tree (package-lock.json, pnpm-lock.yaml, requirements.txt, go.sum, etc.) for undici, including transitive dependencies — a direct dependency you never call can still pull in a vulnerable version.
Fix
Update undici to 7.29.1 or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms CVE-2026-84961 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.
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.
This flaw only affects applications that construct an undici BalancedPool with a function-valued connect or tls option — for example, a custom checkServerIdentity callback or connector used for certificate pinning across multiple upstreams. Client, Pool, Agent, and RoundRobinPool destructure these options before the…
Applications that do not use BalancedPool, or that use it without a custom function-valued connect/tls option, are not affected and require no action. As a workaround until packages are updated, avoid using BalancedPool for any connection that relies on custom TLS certificate validation (e.g. certificate pinning); use Client, Pool, or Agent instead, which are unaffected. The permanent fix is upgrading undici to 7.29.1 or later (7.x line) or 8.10.2 or later (8.x line).Source: Red Hat security advisory for CVE-2026-84961 (CC BY 4.0)
| Product | Fixed in | Advisory |
|---|---|---|
| Red Hat Enterprise Linux 10 | nodejs24-1:24.21.0-1.el10_2 | RHSA-2026:73428 |
| Red Hat Enterprise Linux 8 | nodejs:24-8100020260921144227.6d880403 | RHSA-2026:74085 |
| Red Hat Enterprise Linux 9 | nodejs:24-9080020260921144317.rhel9 | RHSA-2026:73838 |
| Cluster Observability Operator 1.5.3 | cluster-observability-operator/logging-console-plugin-pf4-rhel9:1790854525 | RHSA-2026:74609 |
| Red Hat Ansible Automation Platform 2.1 | ansible-automation-platform/automation-portal:1791295379 | RHSA-2026:80603 |
| Red Hat Ansible Automation Platform 2.2 | ansible-automation-platform/automation-portal:1791293780 | RHSA-2026:80644 |
| Red Hat Ansible Automation Platform 2.2 | ansible-automation-platform/bootc-automation-portal-rhel9:1791865660 | RHSA-2026:82151 |
| Red Hat Developer Hub 1.10 | rhdh/red-hat-developer-hub-backstage-plugin-lightspeed-backend:1791242697 | RHSA-2026:76788 |
Frequently Asked Questions
Is CVE-2026-84961 in your dependencies?
Find it across npm, including transitive dependencies.