uhttpd vulnerable to HTTP request smuggling via invalid chunk-length state reset

published 2026-10-30 9 d ago modified 2026-11-02 6 d ago also EUVD-2026-114561

cvss: 3.7; 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

uhttpd is a small HTTP server. In unpatched repository snapshots, `client_poll_post_data()` in `client.c` consumes an invalid chunk-length line, such as a size exceeding INT_MAX, then clears `r->content_length` and `r->transfer_chunked` without draining the remaining body or setting `request.connection_close`. The completion check treats the chunked POST as finished and the keep-alive parser returns to `CLIENT_STATE_INIT`. Attacker-controlled body bytes aligned as a complete HTTP request are then parsed and processed as another request on the same connection, causing HTTP request smuggling and request-boundary desynchronization. Commits b78f518478794e16ba3568fc1258e40bf3e8eb3b and 34460b8211d676ef1b9f40d6b775c5e112933690 patch the issue.

Patch / fix

links 2

github.com/openwrt/uhttpd@34460b8 commit
github.com/openwrt/uhttpd@b78f518 commit

CISA SSVC

Exploitation: none
Automatable: no
Technical impact: partial
Assessed: 6 d ago (2026-11-02)

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

Affected products

openwrt uhttpd

Classification

Weakness

CWE-444 Inconsistent Interpretation of HTTP Requests

References

Sources

CVE List CVE-2026-55612
NVD CVE-2026-55612

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Summary