CVE-2026-109841 (CVSS 5.9)

Description

undici is an HTTP client library for Node.js. In versions 7.15.0 through 7.30.0 and 8.0.0 through 8.12.1, its fetch() implementation verifies Subresource Integrity metadata by matching the algorithm token against a lowercase-only set, even though the SRI specification defines the token by its ASCII-lowercase form, so a valid but non-lowercase token such as an uppercase or mixed-case SHA256 is treated as unknown and skipped. When no recognized algorithm remains, undici treats the integrity list as empty and accepts the response, so a server returning a body that does not match the pinned digest passes the check. An attacker who controls only the response body can therefore deliver attacker-controlled bytes to an application that pinned a valid uppercase or mixed-case SRI token, with no integrity error, affecting response integrity only. The issue is fixed in undici 7.30.1 and 8.12.2, which normalize the algorithm token to ASCII lowercase before validation, and users should upgrade to one of those versions or later. As a workaround, use lowercase algorithm tokens such as sha256, sha384, or sha512 in integrity metadata.

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CVSS v3.1 Score

5.9

MEDIUM

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

Weakness Type (CWE)

CWE-178 CWE-178

References

Other References

https://cna.openjsf.org/security-advisories.html https://github.com/nodejs/undici/security/advisories/GHSA-f72v-6w45-q472

Frequently Asked Questions

What is CVE-2026-109841? +

undici is an HTTP client library for Node.js. In versions 7.15.0 through 7.30.0 and 8.0.0 through 8.12.1, its fetch() implementation verifies Subresource Integrity metadata by matching the algorithm token against a lowercase-only set, even though the SRI specification defines the token by its ASCII-lowercase form, so a valid but non-lowercase token such as an uppercase or mixed-case SHA256 is treated as unknown and skipped. When no recognized algorithm remains, undici treats the integrity list as empty and accepts the response, so a server returning a body that does not match the pinned digest passes the check. An attacker who controls only the response body can therefore deliver attacker-controlled bytes to an application that pinned a valid uppercase or mixed-case SRI token, with no integrity error, affecting response integrity only. The issue is fixed in undici 7.30.1 and 8.12.2, which normalize the algorithm token to ASCII lowercase before validation, and users should upgrade to one of those versions or later. As a workaround, use lowercase algorithm tokens such as sha256, sha384, or sha512 in integrity metadata. It has a CVSS v3.1 base score of 5.9 (MEDIUM).

How severe is CVE-2026-109841? +

CVE-2026-109841 has a CVSS v3.1 score of 5.9 out of 10, rated MEDIUM. This is a medium-severity vulnerability that should be remediated as part of regular maintenance.

How do I check if I'm vulnerable to CVE-2026-109841? +

You can use Secably's free Website Scanner to check your website for known vulnerabilities. For infrastructure scanning, use the Port Scanner to identify exposed services that may be affected. Check the vendor advisories linked above for specific patch and version information.

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