Mongoose: HTTP/1.0 detection off-by-one enables request smuggling via chunked TE (CVE-2026-73256) | HOL Guard CVE

Unknown severity · Source severity not reportedCVE-2026-73256

Mongoose: HTTP/1.0 detection off-by-one enables request smuggling via chunked TE

Answer in brief

CVE-2026-73256 records a Unknown severity vulnerability in Mongoose: HTTP/1.0 detection off-by-one enables request smuggling via chunked TE. The current sources do not mark it as known exploited. The current feed maps cesanta/mongoose (generic). Check affected ranges and fixed versions before updating.

Analysis pending evidence review

HOL Guard separates source facts from reviewed analysis. See the methodology.

Published Aug 20, 2026Updated Aug 20, 2026Source checked Aug 20, 2026First seen by HOL Aug 20, 2026Material review Aug 20, 2026

Upstream Advisory

Key facts

Risk: Unknown severitySource severity not reported
Exploitation: Not marked as known exploited
Affected software: 1 mapped package or product
Fix availability: Not reported

Why this deserves its current priority

A CVSS score is not reported in the current record. The current sources do not mark it as known exploited. Treat this as a source-backed prioritization signal, not a statement about your environment.

Analysis status

Analysis pending evidence review

Factual feed record only; HOL analysis is not approved for indexing. Read the methodology.

Affected scope and exposure questions

The current feed maps cesanta/mongoose (generic). Check affected ranges and fixed versions before updating.

Mapped affected packages and fixed versions
Package	Affected range	Fixed version
cesanta/mongoosegeneric	< 7.22	Not reported

Recommended response

Check inventory. Check lockfiles and deployed manifests for cesanta/mongoose.
Review the reported fix. Monitor this advisory for an available fix and review any installs of the affected package.

Evidence timeline and material changes

Published upstream
Aug 20, 2026
Evidence: source:cvelist:source_dates:source-dates:record
Source modified
Aug 20, 2026
Evidence: source:cvelist:source_dates:source-dates:record
First seen by HOL
Aug 20, 2026

Sources and claim methodology

Upstream source description

Mongoose is an embedded web server and network library. Prior to 7.22, a remote unauthenticated attacker can exploit an HTTP/1.0 reverse-proxy deployment by sending a request with Transfer-Encoding: chunked and conflicting framing. The http_cb() function in src/http.c tests hm.proto.len with an impossible greater-than-eight condition even though mg_http_parse() requires an eight-byte protocol string, so is_http_1_0 is never set. Mongoose consequently processes chunked encoding that an HTTP/1.0 proxy can ignore, enabling request smuggling and unauthorized access or state changes. This issue is fixed in version 7.22.

Quoted source text, attributed separately from HOL analysis.