VulnerabilityPublished 27 Oct 2026

CVE-2026-109383: undici vulnerable to TLS certificate validation bypass via dropped tls options in Agent

Affects undiciSource GCVE Database

Mentioned vulnerabilities

CVE-2026-84961

Not known to be exploited · CVSS 7.4 High : upgrade to 6.29.1 soon.

Data as of 27 Oct 2026, 20:28 UTC

CVSS 3.1 base score

7.4High

How severe the flaw is on the 0–10 CVSS scale.

Patch: Available – fixed in 6.29.1, 7.30.1, 8.12.2

CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:H/A:N

Attack Vector: Network
Attack Complexity: High
Privileges Required: None
User Interaction: None
Scope: Unchanged
Confidentiality: High
Integrity: High
Availability: None

Bold values are the worst case: easiest to exploit or largest impact.

Attack Vector: Network: The vulnerable component is bound to the network stack and the set of possible attackers extends beyond the other options listed, up to and including the entire Internet. Such a vulnerability is often termed 'remotely exploitable' and can be thought of as an attack being exploitable at the protocol level one or more network hops away (e.g., across one or more routers).
Attack Complexity: High: A successful attack depends on conditions beyond the attacker's control. That is, a successful attack cannot be accomplished at will, but requires the attacker to invest in some measurable amount of effort in preparation or execution against the vulnerable component before a successful attack can be expected. For example, a successful attack may require an attacker to: gather knowledge about the environment in which the vulnerable target/component exists; prepare the target environment to improve exploit reliability; or inject themselves into the logical network path between the target and the resource requested by the victim in order to read and/or modify network communications (e.g., a man in the middle attack).
Privileges Required: None: The attacker is unauthorized prior to attack, and therefore does not require any access to settings or files to carry out an attack.
User Interaction: None: The vulnerable system can be exploited without any interaction from any user.
Scope: Unchanged: An exploited vulnerability can only affect resources managed by the same security authority. In this case, the vulnerable component and the impacted component are either the same, or both are managed by the same security authority.
Confidentiality: High: There is total loss of confidentiality, resulting in all resources within the impacted component being divulged to the attacker. Alternatively, access to only some restricted information is obtained, but the disclosed information presents a direct, serious impact.
Integrity: High: There is a total loss of integrity, or a complete loss of protection. For example, the attacker is able to modify any/all files protected by the impacted component. Alternatively, only some files can be modified, but malicious modification would present a direct, serious consequence to the impacted component.
Availability: None: There is no impact to availability within the impacted component.

Definitions: FIRST CVSS v3.1 specification.

Exploitation evidence

Disclosed: evidence found.
CVE published 27 Oct 2026
Detectable: no evidence on record.
No public nuclei template indexed
Weaponised: no evidence on record.
No public exploit code indexed in Metasploit or Exploit-DB
Exploited in the wildExploited: no evidence on record.
Not in CISA KEV and no source reports exploitation
Observed by OffSeq MirageSeen by Mirage: no evidence on record.
No attack traffic recorded by OffSeq Mirage sensors

A missing step is not evidence of safety. Sources: cve.org (opens in a new tab), the Metasploit, Exploit-DB and nuclei-templates index as of 26 Oct 2026.

Disclosed: The CVE record is public on cve.org. Its publication is t = 0.
Detectable: A public nuclei template can find exposed instances, for defenders and attackers alike.
Weaponised: Public exploit code exists in Metasploit or Exploit-DB, or CISA SSVC or the CVSS exploit maturity reports a public proof of concept.
Exploited in the wild: CISA KEV lists it, CISA SSVC rates exploitation active, or a source reports attacks.
Observed by OffSeq Mirage: OffSeq Mirage honeypot sensors recorded attack traffic for this CVE, or found exposed hosts without attack traffic.

Moments are spaced evenly, not to scale; a dashed line marks a gap of six months or more. Deltas count from t = 0. Sources that give only a date (CISA KEV, Exploit-DB, or a time of exactly 00:00Z) read “same day” rather than hours. Metasploit modules carry the flaw’s disclosure date, not their release date, and nuclei templates carry no date, so both appear above but not on the timeline.

What to do

Upgrade undici to 6.29.1; undici to 7.30.1; undici to 8.12.2.

Affected software

Product	Affected	Fixed in
npmundici	Affected >=4.0.0 <6.29.1	Fixed in 6.29.1
npmundici	Affected >=7.0.0 <7.30.1	Fixed in 7.30.1
npmundici	Affected >=8.0.0 <8.12.2	Fixed in 8.12.2

Check your own hosts for these packages with threat-finder (opens in a new tab), our free open-source scanner.

AI-suggested

Upgrade undici to version 6.29.1, 7.30.1, or 8.12.2 or later, where the Agent preserves the tls option outside the JSON clone, ensuring custom TLS verification callbacks are forwarded correctly. As a workaround, pass TLS options through connect instead of tls. For proxied EnvHttpProxyAgent destinations, use requestTls or proxyTls options. No other actions are required if these mitigations are applied.

Description

undici's Agent component improperly handles TLS options by deep cloning constructor options via JSON serialization, which drops function-valued TLS callbacks such as checkServerIdentity. This results in a TLS certificate validation bypass where custom verification logic is ignored, potentially allowing acceptance of TLS peers that should be rejected. The vulnerability affects applications using Agent as the default dispatcher for request, fetch, and setGlobalDispatcher, as well as EnvHttpProxyAgent on certain routes. Fixed in undici versions 6.29.1, 7.30.1, and 8.12.2.

Impact

Applications that rely on passing a function-valued tls option, such as a custom checkServerIdentity callback for certificate or public-key pinning, are vulnerable to TLS certificate validation bypass. This can allow acceptance of TLS peers with certificates that should be rejected by custom validation logic, potentially enabling man-in-the-middle or spoofing attacks. The vulnerability does not affect applications that do not use custom TLS verification callbacks or that pass TLS options through connect. The severity is high with a CVSS score of 7.4.

CWE-295Improper Certificate Validation (opens in a new tab)
Base weaknessOWASP Top 10 A07:2025: Authentication Failures (opens in a new tab)
The product does not validate, or incorrectly validates, a certificate.
Architecture and Design · Implementation
Certificates should be carefully managed and checked to assure that data are encrypted with the intended owner's public key.
Implementation
If certificate pinning is being used, ensure that all relevant properties of the certificate are fully validated before the certificate is pinned, including the hostname.
OWASP Cheat Sheets
Transport Layer Protection (opens in a new tab)
TLS Cipher String (opens in a new tab)
OWASP Authentication (opens in a new tab)
OWASP ASVS 4.0.3
V9.2.1 (opens in a new tab)
V1.9.2 (opens in a new tab)
V2.8.5 (opens in a new tab)
Attack patterns
Creating a Rogue Certification Authority Certificate (opens in a new tab)
Signature Spoofing by Improper Validation (opens in a new tab)
From MITRE CWE, MITRE CAPEC and OWASP (Top 10, OpenCRE).

References

Community reviews

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Exploitation evidence

What to do

Affected software

Description

AI analysisMachine-generated, updated 27 Oct 2026, 20:28 UTC

WeaknessesCWE-295

Technical details

References

Community reviews

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