CVE-2026-73252

Deferred Deferred - Pending Action

Heap Out-of-Bounds Read in Mongoose TLS Stack

Publication date: 2026-10-14

Last updated on: 2026-10-16

Assigner: GitHub, Inc.

Description

Mongoose is an embedded web server and network library. Prior to 7.23, the built-in TLS stack selected by MG_TLS_BUILTIN in src/tls_builtin.c accepts a TLS 1.3 record whose decrypted size is exactly the 16-byte authentication tag with no plaintext or ContentType byte. In mg_tls_recv_record(), the msgsz length check permits that record and the recv_len calculation underflows to SIZE_MAX, so a later handshake step treats stale buffer contents as a trusted message with an effectively unbounded length. An unauthenticated malicious TLS peer can trigger a heap out-of-bounds read before certificate or Finished validation, causing a remote denial of service. This issue is fixed in version 7.23.

CVSS Scores

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Meta Information

Published

2026-10-14

Last Modified

2026-10-16

Generated

2026-10-19

AI Q&A

2026-10-15

EPSS Evaluated

2026-10-18

NVD

CVE-2026-73252

EUVD

EUVD-2026-101596

Affected Vendors & Products

Vendor	Product	Version / Range
cesanta	mongoose	< 7.23

Helpful Resources

Exploitability

CWE

KEV

CWE ID	Description
CWE-125	The product reads data past the end, or before the beginning, of the intended buffer.
CWE-191	The product subtracts one value from another, such that the result is less than the minimum allowable integer value, which produces a value that is not equal to the correct result.

Attack-Flow Graph

Executive Summary

This vulnerability is an unauthenticated remote heap out-of-bounds read in the built-in TLS stack of the Mongoose library. It occurs due to an off-by-one length check in the mg_tls_recv_record function, which incorrectly allows a TLS 1.3 record with a decrypted size of exactly 16 bytes. This causes an underflow in the recv_len calculation, setting it to SIZE_MAX. The next function call then treats stale buffer bytes as a trusted decrypted message, leading to an attacker-controlled heap over-read.

Detection Guidance

To detect this vulnerability, check the version of Mongoose library in use. If it is version 7.22 or earlier, the system is vulnerable. Commands like 'find / -name mongoose.c 2>/dev/null' or 'ldd <binary> | grep mongoose' may help locate the library. Inspect the source code for the mg_tls_recv_record function to verify if the minimum message size check is set to 17 bytes or higher.

Impact Analysis

An attacker can exploit this flaw to trigger a heap out-of-bounds read before certificate or Finished validation, causing a remote denial of service. The vulnerability is exploitable by any TLS peer, including malicious servers or clients, and may also lead to potential information disclosure.

Compliance Impact

This vulnerability could impact compliance with GDPR and HIPAA by enabling remote denial-of-service attacks or potential information disclosure through heap out-of-bounds reads. GDPR requires data protection and availability, while HIPAA mandates safeguards against unauthorized access or disruptions. The flaw's exploitation could lead to service unavailability or unauthorized data exposure, violating these standards.

Mitigation Strategies

Upgrade Mongoose to version 7.23 or later to address the vulnerability. Monitor network traffic for unusual TLS handshake patterns or crashes in Mongoose-based applications.

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