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Fencer Vulns
medium 4.8

CVE-2026-16728 json

undici vulnerable to downstream response desynchronization via retry interceptor

published 2026-07-29 3 mo ago modified 2026-09-10 1 mo ago also GHSA-8xcm-r25x-g524 , EUVD-2026-50566

cvss
4.8
version 3.1, CNA
cisa kev
Not listed
not in CISA's catalog
epss
0.3%
EPSS 0.3% chance of exploitation in 30 days, percentile 21%
public exploits
0
none known

Summary

undici's retry interceptor can deliver a response whose body length does not match the Content-Length header exposed to the application after a retry or resume of a partial response. In undici before 6.28.0, from 7.0.0 up to before 7.29.0, and from 8.0.0 up to before 8.9.0, a malicious or faulty upstream can return a partial response with a mismatched framing header, close the socket early, and have the retry interceptor assemble a body of a different length while the original Content-Length stays attached. Applications that use the retry interceptor and forward upstream headers and bodies downstream, such as proxies or gateways, may then emit an invalid HTTP response with a stale Content-Length, leading to downstream response desynchronization, connection hangs, or response corruption. Exploitation requires the retry interceptor enabled, an upstream returning a mismatched partial response, and a downstream forwarder that does not remove or recalculate Content-Length. The issue is fixed in undici 6.28.0, 7.29.0, and 8.9.0.

Patch / fix

  • npm undici 6.28.0, 7.29.0, 8.9.0
  • undici undici 6.28.0, 7.29.0, 8.9.0
  • node-undici Debian 14 8.9.0+dfsg+~cs3.2.0-1

debian advisories DEBIAN-CVE-2026-16728

  • nodejs24 hummingbird 1 24.18.1-0.1.hum1
  • nodejs24-bin hummingbird 1 24.18.1-0.1.hum1
  • nodejs24-npm hummingbird 1 11.16.0-1.24.18.1.0.1.hum1
  • nodejs24-libs hummingbird 1 24.18.1-0.1.hum1
  • nodejs24-npm-bin hummingbird 1 24.18.1-0.1.hum1
  • nodejs24-full-i18n hummingbird 1 24.18.1-0.1.hum1
  • nodejs26 hummingbird 1 26.5.1-1.5.hum1
  • nodejs26-bin hummingbird 1 26.5.1-1.5.hum1

red hat advisories RHSA-2026:48537RHSA-2026:48273

  • nodejs18 SLES for SAP 15 SP5, SLES for SAP 15 SP4, SLES 15 SP5-LTSS +5 more 18.20.8-150400.9.39.1
  • nodejs20 SLES for SAP 15 SP5, SLES 15 SP5-LTSS, SLE High Performance Computing 15 SP5-LTSS +1 more 20.20.2-150500.11.30.1
  • nodejs18 SLES LTSS Extended Security 12 SP5, SLES 12 SP5-LTSS 18.20.8-8.44.1
  • nodejs20 SLES for SAP 15 SP6, SLES 15 SP6-LTSS 20.20.2-150600.3.21.1

suse advisories SUSE-SU-2026:4261-1SUSE-SU-2026:4248-1SUSE-SU-2026:3930-1SUSE-SU-2026:3929-1

Vendor advisories

What the vendors themselves say about their products: affected, fixed or not affected, and what to do.

red hat product security vex CVE-2026-16728 updated cvss 4.8

undici: undici: Response desynchronization via retry interceptor with mismatched Content-Length

  • Red Hat Hardened Images nodejs25 25.9.0-1.5.hum1
    affected: no fix planned “Will not fix”
  • Red Hat Hardened Images nodejs26 26.5.1-1.5.hum1, nodejs24 24.18.1-0.1.hum1, nodejs26-bin 26.5.1-1.5.hum1, nodejs24-bin 24.18.1-0.1.hum1, nodejs26-libs 26.5.1-1.5.hum1, nodejs24-libs 24.18.1-0.1.hum1, +6 more
    fixed: vendor fix RHSA-2026:48537
  • Red Hat Hardened Images rust 1.97.1-2.hum1, jaeger 2.20.0-0.6.hum1, grafana12.4 12.4.6-0.2.hum1, prometheus3.13 3.13.1-0.4.hum1
    not affected: vulnerable code not present

Red Hat CSAF VEX © Red Hat, Inc., from https://security.access.redhat.com/data/csaf/v2/vex/; changed: reduced to product statuses and remediations. CC BY 4.0 · csaf

CISA SSVC

Exploitation
none
Automatable
no
Technical impact
partial
Assessed
3 mo ago

Exploit prediction

0.29% chance of exploitation in the next 30 days, higher than 21% of all scored CVEs (FIRST EPSS, 2026-11-08).

CVSS scores

assigned by version score vector
CNA 3.1 4.8 CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:L/I:L/A:N
NVD 3.1 6.5 CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:L/A:L
GitHub 3.1 4.8 CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:L/I:L/A:N

Affected packages

ecosystem package affected fixed in
npm undici
<6.28.0
>=7.0.0, <7.29.0
>=8.0.0, <8.9.0
6.28.0
7.29.0
8.9.0

Affected products

  • undici undici

Classification

Weakness
  • CWE-444 Inconsistent Interpretation of HTTP Requests

References

Sources

Fencer Vulns keeps one entry per vulnerability: the CVE id wins, then GHSA, and records that alias each other are merged, except that two CVEs always keep separate entries. The same data is available as JSON.