CVE-2026-73256
Mongoose: HTTP/1.0 detection off-by-one enables request smuggling via chunked TE
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.
INFO
Published Date :
Aug. 20, 2026, 6:16 p.m.
Last Modified :
Sept. 29, 2026, 3:39 p.m.
Remotely Exploit :
Yes !
Source :
[email protected]
CVSS Scores
| Score | Version | Severity | Vector | Exploitability Score | Impact Score | Source |
|---|---|---|---|---|---|---|
| CVSS | 134c704f-9b21-4f2e-91b3-4a467353bcc0 | |||||
| CVSS 3.1 | CRITICAL | [email protected] | ||||
| CVSS 3.1 | CRITICAL | MITRE-CVE |
Solution
- Update Mongoose to version 7.22 or later.
- Ensure proper HTTP protocol handling configurations.
- Validate proxy and server communication protocols.
- Review HTTP framing and encoding implementations.
References to Advisories, Solutions, and Tools
Here, you will find a curated list of external links that provide in-depth
information, practical solutions, and valuable tools related to
CVE-2026-73256.
| URL | Resource |
|---|---|
| https://github.com/cesanta/mongoose/commit/a9df523f76f43a38bd53b4232b9cfd4c16869e71 | Patch |
| https://github.com/cesanta/mongoose/pull/3611 | Issue Tracking Patch |
| https://github.com/cesanta/mongoose/releases/tag/7.22 | Release Notes |
| https://github.com/cesanta/mongoose/security/advisories/GHSA-mgp5-rjrv-h5j3 | Exploit Vendor Advisory |
CWE - Common Weakness Enumeration
While CVE identifies
specific instances of vulnerabilities, CWE categorizes the common flaws or
weaknesses that can lead to vulnerabilities. CVE-2026-73256 is
associated with the following CWEs:
Common Attack Pattern Enumeration and Classification (CAPEC)
Common Attack Pattern Enumeration and Classification
(CAPEC)
stores attack patterns, which are descriptions of the common attributes and
approaches employed by adversaries to exploit the CVE-2026-73256
weaknesses.
We scan GitHub repositories to detect new proof-of-concept exploits. Following list is a collection of public exploits and proof-of-concepts, which have been published on GitHub (sorted by the most recently updated).
Results are limited to the first 15 repositories due to potential performance issues.
The following list is the news that have been mention
CVE-2026-73256 vulnerability anywhere in the article.
The following table lists the changes that have been made to the
CVE-2026-73256 vulnerability over time.
Vulnerability history details can be useful for understanding the evolution of a vulnerability, and for identifying the most recent changes that may impact the vulnerability's severity, exploitability, or other characteristics.
-
Initial Analysis by [email protected]
Sep. 29, 2026
Action Type Old Value New Value Added CPE Configuration OR *cpe:2.3:a:cesanta:mongoose:*:*:*:*:*:*:*:* versions up to (excluding) 7.22 Added Reference Type GitHub, Inc.: https://github.com/cesanta/mongoose/commit/a9df523f76f43a38bd53b4232b9cfd4c16869e71 Types: Patch Added Reference Type GitHub, Inc.: https://github.com/cesanta/mongoose/pull/3611 Types: Issue Tracking, Patch Added Reference Type GitHub, Inc.: https://github.com/cesanta/mongoose/releases/tag/7.22 Types: Release Notes Added Reference Type GitHub, Inc.: https://github.com/cesanta/mongoose/security/advisories/GHSA-mgp5-rjrv-h5j3 Types: Exploit, Vendor Advisory -
CVE Modified by 134c704f-9b21-4f2e-91b3-4a467353bcc0
Aug. 21, 2026
Action Type Old Value New Value Added SSVC {'id': 'CVE-2026-73256', 'role': 'CISA Coordinator', 'options': [{'exploitation': 'none'}, {'automatable': 'yes'}, {'technicalImpact': 'total'}], 'version': '2.0.3', 'timestamp': '2026-08-21T21:10:40.015064Z'} -
New CVE Received by [email protected]
Aug. 20, 2026
Action Type Old Value New Value Added Affected [{'vendor': 'cesanta', 'product': 'mongoose', 'versions': [{'status': 'affected', 'version': '< 7.22'}]}] Added 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. Added CVSS V3.1 AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:N Added CWE CWE-444 Added Reference https://github.com/cesanta/mongoose/commit/a9df523f76f43a38bd53b4232b9cfd4c16869e71 Added Reference https://github.com/cesanta/mongoose/pull/3611 Added Reference https://github.com/cesanta/mongoose/releases/tag/7.22 Added Reference https://github.com/cesanta/mongoose/security/advisories/GHSA-mgp5-rjrv-h5j3