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Mongoose CVE-2021-26529

CRITICAL
Out-of-bounds Write (CWE-787)
2021-02-08 cve@mitre.org
9.1
CVSS 3.1 · NVD
View

Vulnerability Assessment

Weakness
CWE
ASVS 5.0
V15 - Secure Coding and Architecture Bounds checking, write limits
MITRE ATT&CK

2 techniques across 2 tactics: Execution, Privilege Escalation

The technique list with ATT&CK links and the kill-chain view is part of the Basic plan and up.

Impact

CVSS score of 9.1 (CRITICAL). Attack characteristics: network attack vector, low complexity, no privileges required, no user interaction not required. Public proof-of-concept exploit code is available.

Exploit ScenarioDerived

A remote attacker could write data beyond allocated buffer boundaries leading to code execution or crashes by sending crafted requests to the affected application. No authentication is required to exploit this vulnerability.

Act Now Prioritize within 24-48h. Why: CRITICAL severity + public POC available.
No patch listed yet 1.5% exploitation probability (EPSS)

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AnalysisAI

The mg_tls_init function in Cesanta Mongoose HTTPS server 7.0 and 6.7-6.18 (compiled with mbedTLS support) is vulnerable to remote OOB write attack via connection request after exhausting memory pool. Rated critical severity (CVSS 9.1), this vulnerability is remotely exploitable, no authentication required, low attack complexity. Public exploit code available and no vendor patch available.

RemediationAI

No vendor patch is available at time of analysis. Monitor vendor advisories for updates. Validate write boundaries, use memory-safe languages, enable compiler protections (ASLR, stack canaries).

Affects your stack

Find out whether the stacks and servers you run are on an affected version.

Checking this CVE against your own stacks and servers is part of the Basic plan and up.

Technical ContextAI · show details

This vulnerability is classified as Out-of-bounds Write (CWE-787), which allows attackers to write data beyond allocated buffer boundaries leading to code execution or crashes. The mg_tls_init function in Cesanta Mongoose HTTPS server 7.0 and 6.7-6.18 (compiled with mbedTLS support) is vulnerable to remote OOB write attack via connection request after exhausting memory pool. Affected products include: Cesanta Mongoose.

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  • Exploit and PoC references, threat intelligence from 22 sources

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Severity by source

NVD PRIMARY 9.1 CRITICAL
AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:H/A:H

Primary rating from NVD · only source for this CVE.

CVSS VectorNVD

Attack Vector
Network
Attack Complexity
Low
Privileges Required
None
User Interaction
None
Scope
Unchanged
Confidentiality
None
Integrity
High
Availability
High

DescriptionNVD

The mg_tls_init function in Cesanta Mongoose HTTPS server 7.0 and 6.7-6.18 (compiled with mbedTLS support) is vulnerable to remote OOB write attack via connection request after exhausting memory pool.

Threat Intelligence Overview

EPSS Score
1.5%
Top 29% exploitable
Exploit
POC
Public exploit code exists
Data Quality
3 sources
Confidence: Low

How this decision was reached

The engine reads each signal below and applies a fixed list of rules from top to bottom. The first rule that matches sets the recommended action – like a statement, every line is shown.

SignalValue
Severity CRITICAL
CISA KEV No
Public POC Yes
EPSS 1.5%
Patch available No
Active threat No
Deciding rule
CRITICAL severity + public POC available
What every action level means
Emergency Immediate action required. Criteria: CRITICAL + in CISA KEV (actively exploited) without patch, OR CRITICAL + EPSS > 30% without patch, OR CRITICAL + active threat signals without patch.
Act Now Prioritize within 24-48h. Criteria: in KEV with patch available, OR CRITICAL + public POC, OR HIGH + EPSS > 10%, OR CRITICAL + active threat, OR any CRITICAL severity.
This Week Schedule remediation this week. Criteria: HIGH severity (CVSS 7.0-8.9). Patch within normal change window.
This Month Plan within 30 days. Criteria: MEDIUM severity (CVSS 4.0-6.9), lower exploitation probability. Include in regular patch cycle.
Monitor Track and reassess. Criteria: LOW severity (CVSS 0.1-3.9), minimal exploitation risk. No immediate action needed.

SSVC AssessmentENISA

SSVC Decision· derived
Scheduled
Exploitation· derived
Poc
System Exposure· derived
Open
Automatable· derived
Yes
Human Impact· derived
Medium

Priority Score

67
Low Medium High Critical
KEV: 0
EPSS: +1
CVSS: +46
PoC: +20
Weaponized: 0
Threat intel: 0
Gov advisory: 0

Attack Technique

A buffer overflow occurs when a program writes more data to a memory buffer than it was allocated to hold, causing the excess data to spill into adjacent memory regions.

Memory corruption occurs when a program writes data beyond the boundaries of allocated memory regions or accesses memory in unintended ways, violating the integrity of the process's address space.

Affected Products (CPE)NVD

cpe:2.3:a:cesanta:mongoose:*:*:*:*:*:*:*:*
cpe:2.3:a:cesanta:mongoose:7.0:*:*:*:*:*:*:*
CVE-2025-23061 CRITICAL POC
9.0 Jan 15

Mongoose ODM for Node.js before version 8.9.5 contains a search injection vulnerability when using $where filters with p

CVE-2017-2894 CRITICAL POC
9.8 Nov 07

An exploitable stack buffer overflow vulnerability exists in the MQTT packet parsing functionality of Cesanta Mongoose 6

CVE-2017-2891 CRITICAL POC
9.8 Nov 07

An exploitable use-after-free vulnerability exists in the HTTP server implementation of Cesanta Mongoose 6.8. Rated crit

CVE-2017-2922 CRITICAL POC
9.8 Nov 07

An exploitable memory corruption vulnerability exists in the Websocket protocol implementation of Cesanta Mongoose 6.8.

CVE-2017-2921 CRITICAL POC
9.8 Nov 07

An exploitable memory corruption vulnerability exists in the Websocket protocol implementation of Cesanta Mongoose 6.8.

CVE-2023-3696 CRITICAL POC
9.8 Jul 17

Prototype Pollution in GitHub repository automattic/mongoose prior to 7.3.4. Rated critical severity (CVSS 9.8), this vu

CVE-2022-2564 CRITICAL POC
9.8 Jul 28

Prototype Pollution in GitHub repository automattic/mongoose prior to 6.4.6. Rated critical severity (CVSS 9.8), this vu

CVE-2019-19307 CRITICAL POC
9.8 Nov 26

An integer overflow in parse_mqtt in mongoose.c in Cesanta Mongoose 6.16 allows an attacker to achieve remote DoS (infin

CVE-2024-53900 CRITICAL POC
9.1 Dec 02

Mongoose before 8.8.3 can improperly use $where in match, leading to search injection. Rated critical severity (CVSS 9.1

CVE-2021-26530 CRITICAL POC
9.1 Feb 08

The mg_tls_init function in Cesanta Mongoose HTTPS server 7.0 (compiled with OpenSSL support) is vulnerable to remote OO

CVE-2021-26528 CRITICAL POC
9.1 Feb 08

The mg_http_serve_file function in Cesanta Mongoose HTTP server 7.0 is vulnerable to remote OOB write attack via connect

CVE-2018-18765 CRITICAL POC
9.1 Oct 29

An exploitable arbitrary memory read vulnerability exists in the MQTT packet-parsing functionality of Cesanta Mongoose 6

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