CVE-2026-55612
LowCVSS 3.7Exploitation Probability (EPSS)
Low risk22th percentile - higher than 22% of all known CVEs
Summary
uhttpd is a small HTTP server. In unpatched repository snapshots, client_poll_post_data() in client.c consumes an invalid chunk-length line (e.g., a size exceeding INT_MAX), then clears r->content_length and r->transfer_chunked without draining the remaining body or setting request.connection_close. 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.
Risk Assessment
Integrity and confidentiality breach — an attacker can smuggle HTTP requests, potentially leading to bypass of security controls, cache poisoning, or session hijacking. This may affect systems using uhttpd.
Recommendation
Update uhttpd to a version containing the fixes (commits b78f518478794e16ba3568fc1258e40bf3e8eb3b and 34460b8211d676ef1b9f40d6b775c5e112933690). Verify server configuration for request smuggling vulnerabilities.
Other vulnerabilities in uhttpd
See all- CVE-2026-63586Critical
The web-based management interface uses a modified uhttpd server with CGI shell scripts. The HTTP Basic Authentication username, taken directly from the Authorization header without sanitization, is inserted into a shell command string executed via the system() function. By submitting a specially crafted username containing shell metacharacters, an unauthenticated attacker with network access to the device can escape the command context and execute arbitrary commands with root privileges.
- CVE-2026-55614Medium
In unpatched uhttpd repository snapshots, `client_parse_header()` compares the `Transfer-Encoding` value to `chunked` case-sensitively, although transfer-coding tokens are case-insensitive. A mixed-case token is accepted without enabling chunked handling, allowing HTTP request smuggling on keep-alive connections.
- CVE-2026-55613Medium
In unpatched uhttpd repository snapshots, `uh_ubus_data_send()` can desynchronize HTTP request boundaries when a `POST /ubus` JSON body arrives in multiple TCP segments. The unread body suffix is then processed as a new request on the same keep-alive connection.
Original NVD description (English source)
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.
Vulnerability data from NVD (NIST) · CISA KEV · EPSS