# CVE-2026-18540

## Summary

- **CVE ID:** CVE-2026-18540
- **Severity:** LOW
- **CVSS Score:** 3.7 (CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:N/I:L/A:N)
- **CWE:** CWE-444
- **Published:** Sep 4, 2026
- **Last Modified:** Sep 4, 2026

## Description

undici's retry interceptor can append the body of a ranged retry response to bytes already delivered from an earlier partial response while still presenting the original response's status and headers. This happens when an upstream server delivers part of a body without a trustworthy resume checkpoint, for example a non-success response whose headers were already sent or a partial-content response with an unusable content range, then closes the connection and answers the resumed range request with more bytes. As a result the response body can be longer than the Content-Length that the application observes. An application that relays such a response to a downstream HTTP/1.1 peer without normalizing the framing can emit a body that exceeds the forwarded Content-Length, and the excess bytes can be interpreted as the start of a following response, which enables downstream response splitting or desynchronization. Exploitation requires an attacker-controlled upstream server and an application that forwards the response through a framing-sensitive path. This affects undici versions before 6.28.1, from 7.0.0 up to 7.29.1, and from 8.0.0 up to 8.10.2. Users should upgrade to undici 6.28.1, 7.29.1, or 8.10.2.

## Affected Products

- undici — undici (0)
- undici — undici (6.28.1)
- undici — undici (7.0.0)
- undici — undici (7.29.1)
- undici — undici (8.0.0)
- undici — undici (8.10.2)

## References

- [CNA](https://github.com/nodejs/undici/security/advisories/GHSA-r53p-7pc4-xj5r)
- [CNA](https://cna.openjsf.org/security-advisories.html)

## Exploitation Prediction (EPSS)

- **EPSS Score:** 0.22%
- **EPSS Percentile:** 12.1

---
_Exported from OnDuty AI Vulnerability Intelligence on 2026-09-09._