undici vulnerable to Denial of Service via TLS 1.2 certificate-changing renegotiation (CVE-2026-87018)

What is affected, what to do

A flaw was found in undici. A remote server can cause a Denial of Service (DoS) by initiating a Transport Layer Security (TLS) renegotiation and presenting a certificate with a mismatched hostname.

Update Undici to version 6.29.1, Undici to version 7.30.1, Undici to version 8.12.2.

Affected

• Undici lt 4.2.1..6.29.1
• Undici lt 7.0.0..7.30.1
• Undici lt 8.0.0..8.12.2

Fixed in

• Undici 6.29.1
• Undici 7.30.1
• Undici 8.12.2

Not sure whether and how you are affected? Ask a question about this vulnerability

Metrics

Detection rules

No NEOSEC detection rule is available for this vulnerability yet.

Classification under NIS2 and CRA

Rule-based classification from exploitation status and severity. It does not replace a case-by-case assessment.

NIS2

NIS2 is EU Directive (EU) 2022/2555 to raise the level of cybersecurity across the Union. It substantially broadens obligations compared with the first NIS directive: more sectors, mandatory risk management, staged reporting duties and personal accountability of senior management.

Read in glossary

High technical severity: assess and remediate the vulnerability in vulnerability handling under Art. 21(2)(e) NIS2 and document the decision.

CRA

The CRA is EU Regulation (EU) 2024/2847 setting horizontal cybersecurity requirements for „products with digital elements“ — from industrial controllers and software to connected consumer devices. For the first time manufacturers must ensure security across the entire product lifecycle, handle vulnerabilities and provide security updates.

Read in glossary

From 11.12.2027, Annex I Part II CRA requires manufacturers of affected products with digital elements to handle vulnerabilities without delay and provide security updates.

ISO/IEC 27001

ISO/IEC 27001 is the internationally leading standard for an information security management system (ISMS). It describes a risk-based, process-oriented framework to systematically plan, implement, review and improve information security.

Read in glossary

Control A.8.8, management of technical vulnerabilities: assess relevance to your systems, plan remediation and keep evidence.

Description

A flaw was found in undici. A remote server can cause a Denial of Service (DoS) by initiating a Transport Layer Security (TLS) renegotiation and presenting a certificate with a mismatched hostname. Because the client application fails to properly handle the resulting verification error, an uncaught assertion is triggered, terminating the client process and disrupting active network requests.

Source: redhat_csaf, OSV (Open Source Vulnerabilities), GitHub Security Advisories, NVD (NIST), cvelistv5

Vendors and products

• NodeJS Nodejs undici
• Undici Undici

Weakness classes (CWE)

• CWE-248Uncaught Exception

  Base

  An exception is thrown from a function, but it is not caught.

  Entry at MITRE CWE-248

• CWE-617Reachable Assertion

  Base

  The product contains an assert() or similar statement that can be triggered by an attacker, which leads to an application exit or other behavior that is more severe than necessary.

  Entry at MITRE CWE-617

References & sources

• github.comnodejs/undici/security/advisories/GHSA-qrxm-fqhp-jwvmVendor advisory, web
• cna.openjsf.orgsecurity-advisories.htmlVendor advisory, web
• NVD (NIST)vuln/detail/CVE-2026-87018advisory
• github.comnodejs/undici/commit/12cfd96c3f430897656e3edc1c5e02be8c1cd309web
• github.comnodejs/undici/commit/b40fbfc0651703cf9fa9f6ced68b679f28d8bb28web
• github.comnodejs/undici/commit/e257e9f8fb42eedd50727b9cf65e548c8925e4a8web
• github.comnodejs/undicipackage
• github.comnodejs/undici/releases/tag/v6.29.1web
• github.comnodejs/undici/releases/tag/v7.30.1web
• github.comnodejs/undici/releases/tag/v8.12.2web

Changes to this CVE

Who changed this CVE and when: NVD (analysis, affected products, CVSS), the CVE publisher (CNA) and additional providers such as CISA (ADP).

1. 19.10.2026Initial analysis by NVDNVD

   Newly listed as affected:

   • Nodejs undici (7.0.0 – before 7.30.1; 8.0.0 – before 8.12.2; 4.2.1 – before 6.29.1)

   New references:

   • https://cna.openjsf.org/security-advisories.html
   • https://github.com/nodejs/undici/security/advisories/GHSA-qrxm-fqhp-jwvm
   Show 3 original changes

   Individual changes of this event as published by NVD

   Type	Action	Before	After
   Product configuration	added	—	OR *cpe:2.3:a:nodejs:undici:*:*:*:*:*:node.js:*:* versions from (including) 7.0.0 up to (excluding) 7.30.1 *cpe:2.3:a:nodejs:undici:*:*:*:*:*:node.js:*:* versions from (including) 8.0.0 up to (excluding) 8.12.2 *cpe:2.3:a:nodejs:undici:*:*:*:*:*:node.js:*:* versions from (including) 4.2.1 up to (excluding) 6.29.1
   Reference type	added	—	openjs: https://cna.openjsf.org/security-advisories.html Types: Vendor Advisory
   Reference type	added	—	openjs: https://github.com/nodejs/undici/security/advisories/GHSA-qrxm-fqhp-jwvm Types: Vendor Advisory

   Source identifier: nvd@nist.gov

2. 16.10.2026Record modifiedCISA ADP

   CISA assessment (SSVC): exploitation: none known, automatable: yes

   Show the original change

   Individual changes of this event as published by NVD

   Type	Action	Before	After
   SSVC assessment	added	—	{"id":"CVE-2026-87018","role":"CISA Coordinator","options":[{"exploitation":"none"},{"automatable":"yes"},{"technicalImpact":"partial"}],"version":"2.0.3","timestamp":"2026-10-16T20:01:12.990357Z"}

   Source identifier: 134c704f-9b21-4f2e-91b3-4a467353bcc0

3. 15.10.2026ReceivedOpenJS Foundation

   CVSS V3.1: AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H

   Weakness type: CWE-248, CWE-617

   Description added or changed

   New references:

   • https://cna.openjsf.org/security-advisories.html
   • https://github.com/nodejs/undici/security/advisories/GHSA-qrxm-fqhp-jwvm
   Show 7 original changes

   Individual changes of this event as published by NVD

   Type	Action	Before	After
   Description	added	—	undici is an HTTP client library for Node.js. In versions 4.2.1 through 6.29.0, 7.0.0 through 7.30.0, and 8.0.0 through 8.12.1, the client process crashes when a TLS 1.2 server renegotiates after the connection is established and presents a different, CA-trusted certificate whose hostname does not match the requested host. Node.js re-runs hostname verification on the renegotiated handshake and destroys the socket with a certificate-altname error, but undici's established-socket error handler asserted that this error code could never occur, so the peer-controlled error became an uncaught assertion that terminates the Node.js process, affecting both the HTTP/1.1 and HTTP/2 paths. A malicious or compromised HTTPS endpoint reached through undici or the global fetch() can crash the client with a single server-initiated renegotiation, taking down all in-flight requests and background work in the process, and exploitation needs no CA compromise because the attacker controls the endpoint and can present two ordinary valid certificates. Only TLS 1.2 is affected, since TLS 1.3 does not support renegotiation. The issue is fixed in undici 6.29.1, 7.30.1, and 8.12.2, and users should upgrade to one of those versions or later. As a workaround, restrict outbound connections to TLS 1.3 so renegotiation cannot occur, when the target endpoints support it.
   CVSS	added	—	AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H
   Weakness type (CWE)	added	—	CWE-248
   Weakness type (CWE)	added	—	CWE-617
   Affected versions (publisher)	added	—	New affected value received. <a href="https://github.com/CVEProject/cvelistV5/blob/main/cves/2026/87xxx/CVE-2026-87018.json">CVE-2026-87018</a>
   Reference	added	—	https://cna.openjsf.org/security-advisories.html
   Reference	added	—	https://github.com/nodejs/undici/security/advisories/GHSA-qrxm-fqhp-jwvm

   Source identifier: ce714d77-add3-4f53-aff5-83d477b104bb