uhttpd: HTTP request smuggling via ubus POST body parse-error desync

published 2026-10-30 9 d ago modified 2026-11-05 4 d ago also EUVD-2026-114522

cvss: 6.9; version 4.0, CNA
cisa kev: Not listed; not in CISA's catalog
epss: 0.4%; EPSS 0.4% chance of exploitation in 30 days, percentile 33%
public exploits: 0; none known

uhttpd is a small HTTP server. In unpatched repository snapshots, `uh_ubus_data_send()` in `ubus.c` can desynchronize HTTP request boundaries when a `POST /ubus` JSON body arrives in multiple TCP segments. An initial segment completing a JSON object sets `du->jsobj`; a later segment takes the existing-object parse-error path and returns zero bytes consumed. The caller neither drains the remaining declared `Content-Length` nor sets `connection_close`. An HTTP request embedded in the unread body suffix is consequently processed as a new request on the same keep-alive connection. The reported reproducer returned a JSON-RPC parse error followed by a second HTTP response. This application-layer body-handler flaw is distinct from Transfer-Encoding header case handling and chunk-length state reset, and affects deployments enabling ubus, including the default OpenWrt configuration and potential proxy/CDN deployments. Repository patches 7b1bec45826bd78c8afc993435bdc0f1df2fe399 and b2285de129b9adc8b12f84f9a27c16c21f2b57a5 address this issue.

Patch / fix

links 2

github.com/openwrt/uhttpd@7b1bec4 commit
github.com/openwrt/uhttpd@b2285de commit

CISA SSVC

Exploitation: Proof of concept is public
Automatable: yes
Technical impact: partial
Assessed: 4 d ago (2026-11-05)

Exploit prediction

0.40% chance of exploitation in the next 30 days, higher than 33% of all scored CVEs (FIRST EPSS, 2026-11-08).

Exploits and checks

github.com https://github.com/openwrt/uhttpd/security/advisories/GHSA-wgwp-64hh-f52p referenced PoC, tagged "exploit" by a source, unverified

CVSS scores

assigned by	version	score	vector
CNA	4.0	6.9	CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:N/VI:L/VA:N/SC:N/SI:N/SA:N
CNA	4.0	6.9	CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:N/VI:L/VA:N/SC:N/SI:N/SA:N/E:X/CR:X/IR:X/AR:X/MAV:X/MAC:X/MAT:X/MPR:X/MUI:X/MVC:X/MVI:X/MVA:X/MSC:X/MSI:X/MSA:X/S:X/AU:X/R:X/V:X/RE:X/U:X

Affected products

openwrt uhttpd

Classification

Weakness

CWE-444 Inconsistent Interpretation of HTTP Requests

References

Sources

CVE List CVE-2026-55613
NVD CVE-2026-55613

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.

Summary