Mongoose is an embedded web server and network library. Prior to 7.23, the built-in TCP/IP stack enabled by MGENABLETCPIP in src/netbuiltin.c does not reject a TCP option whose declared opts[1] length exceeds the remaining option bytes. In handleopt(), a NOP followed by a truncated MSS option causes opts[3] to be read outside the declared options area and used as the low byte of dmss. An unauthenticated remote peer can corrupt the per-connection MSS value so later mgsend() calls transmit truncated or zero-length application payloads while the TCP connection otherwise appears healthy. This issue is fixed in version 7.23.

Mongoose is an embedded web server and network library. Prior to 7.23, the built-in TLS stack selected by MGTLSBUILTIN in src/tlsbuiltin.c accepts a TLS 1.3 record whose decrypted size is exactly the 16-byte authentication tag with no plaintext or ContentType byte. In mgtlsrecvrecord(), the msgsz length check permits that record and the recvlen calculation underflows to SIZEMAX, 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.

A weakness has been identified in Cesanta Mongoose up to 7.21. Affected by this vulnerability is the function fn of the file tutorials/mqtt/mqtt-server/main.c of the component MQTT Broker. Executing a manipulation can lead to stack-based buffer overflow. The attack can be launched remotely. The exploit has been made available to the public and could be used for attacks. Upgrading to version 7.22 addresses this issue. This patch is called a9df523f76f43a38bd53b4232b9cfd4c16869e71. Upgrading the affected component is advised.

Mongoose is an embedded web server and network library. Prior to version 7.22, an on-path network attacker with a wildcard certificate for a parent domain can impersonate deeper subdomains to a client using the built-in TLS stack. The mgtlsverifycertsan() and mgtlsverifycertcn() functions in src/tlsbuiltin.c call mgmatch(), whose wildcard can cross DNS label boundaries, so a pattern such as .example.com can match foo.bar.example.com. The resulting hostname verification bypass permits interception and modification of TLS traffic. This issue is fixed in version 7.22.

Mongoose is an embedded web server and network library. Prior to 7.22, an attacker who can control an SSI-enabled file can place directory traversal sequences in an #include file or #include virtual directive. The mgssi() function in src/ssi.c concatenates the directive argument into a filesystem path without calling mgpathissane(), allowing an MGENABLESSI deployment with ssipattern configured to disclose files readable by the Mongoose process. This issue is fixed in version 7.22.

Mongoose is an embedded web server and network library. Prior to 7.22, a remote attacker can send a crafted percent-encoded request path to a deployment using MGENABLEDIRLIST and persuade a user to visit it. The mghttpservedir() and listdir() path in src/http.c places the decoded request URI into the title and h1 elements without HTML entity encoding. The resulting reflected cross-site scripting executes in the Mongoose origin and can expose session data or perform actions as the victim. This issue is fixed in version 7.22.

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 httpcb() function in src/http.c tests hm.proto.len with an impossible greater-than-eight condition even though mghttpparse() requires an eight-byte protocol string, so ishttp10 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.

Mongoose is an embedded web server and network library. Prior to 7.22, an attacker who can create a file with an HTML payload in its name can trigger stored cross-site scripting when a user browses a directory served with MGENABLEDIRLIST. The printdirentry() path called by listdir() in src/http.c URL-encodes the href but inserts the raw filesystem filename into the HTML link text. The browser executes the injected markup in the Mongoose origin, which can expose session data or permit actions as the victim. This issue is fixed in version 7.22.

Mongoose is an embedded web server and network library. Prior to 7.22, a remote attacker can place a lone carriage return or line feed in multipart input processed by mghttpnextmultipart() in src/http.c. The loops comparing s[b] and s[b + 1], and s[h2] and s[h2 + 1], use an incorrect AND condition and stop when either character resembles part of a CRLF terminator. This truncates headers, filenames, or boundaries and can cause an application to accept dangerous content after seeing a misleading Content-Type value. This issue is fixed in version 7.22.

Mongoose is an embedded web server and network library. Prior to 7.23, a network attacker can impersonate a TLS server to a Mongoose client configured with a multi-certificate CA bundle. In src/tlsbuiltin.c, the mgtlsinit() function stores the bundle in tls->cabundleder while tls->cader.len remains zero, and mgtlsrecvcert() uses tlsbundlefind() to accept a Common Name match without calling mgtlsverifycertsignature(). A forged self-signed certificate can therefore satisfy hostname and CertificateVerify checks and enable interception, credential disclosure, traffic modification, and malicious responses. This issue is fixed in version 7.23.

Mongoose is an embedded web server and network library. Priro to version 7.22, a remote unauthenticated attacker can send an HTTP request containing both Content-Length and Transfer-Encoding: chunked. The clcount and tecount checks in the mghttpparse() and httpcb() paths in src/http.c accept both headers and prioritize chunked encoding, while a Content-Length-preferring reverse proxy can use a different request boundary. This CL.TE desynchronization can inject requests that access or modify resources in another user context. This issue is fixed in version 7.22.

Cesanta Mongoose before 7.22 contains an out-of-bounds read in the built-in TLS server function mgtlsserverrecvhello(), which uses an attacker-controlled sessionidlen byte from a TLS ClientHello as a buffer index without validating it against the length of received data. A remote, unauthenticated attacker can send a single crafted ClientHello with an oversized session id length to read past the receive buffer, crashing any HTTPS, MQTTS, or WSS service built on MGTLSBUILTIN.

A security vulnerability has been detected in Cesanta Mongoose up to 7.20. This issue affects the function mgaesgcmdecrypt of the file /src/tlsaes128.c of the component GCM Authentication Tag Handler. Such manipulation leads to improper verification of cryptographic signature. The attack may be performed from remote. A high complexity level is associated with this attack. The exploitability is assessed as difficult. The exploit has been disclosed publicly and may be used. Upgrading to version 7.21 is capable of addressing this issue. It is advisable to upgrade the affected component. VulDB has contacted the vendor early and they confirmed quickly, that this issue got fixed already.

A weakness has been identified in Cesanta Mongoose up to 7.20. This vulnerability affects the function handleopt of the file /src/netbuiltin.c of the component TCP Option Handler. This manipulation of the argument optlen causes infinite loop. The attack is possible to be carried out remotely. The exploit has been made available to the public and could be used for attacks. Upgrading to version 7.21 is able to resolve this issue. Upgrading the affected component is advised. VulDB has contacted the vendor early and they confirmed quickly, that this issue got fixed already.

Mongoose network library <= 7.20 CVE-2026-5244 - mg\tls\recv\cert pubkey heap-based overflow (exploitable) CVE-2026-5245 - mDNS Record stack-based overflow (exploitable) CVE-2026-5246 - authorization bypass via P-384 Public Key (trivially exploitable)

Fun ride.

A vulnerability was determined in Cesanta Mongoose up to 7.20. Affected is the function mgtlsverifycertsignature of the file mongoose.c of the component P-384 Public Key Handler. Executing a manipulation can lead to authorization bypass. The attack can be executed remotely. Attacks of this nature are highly complex. The exploitability is told to be difficult. The exploit has been publicly disclosed and may be utilized. Upgrading to version 7.21 is able to address this issue. This patch is called 0d882f1b43ff2308b7486a56a9d60cd6dba8a3f1. The affected component should be upgraded. The vendor was contacted early, responded in a very professional manner and quickly released a fixed version of the affected product.

A vulnerability was found in Cesanta Mongoose up to 7.20. This impacts the function handlemdnsrecord of the file mongoose.c of the component mDNS Record Handler. Performing a manipulation of the argument buf results in stack-based buffer overflow. Remote exploitation of the attack is possible. A high degree of complexity is needed for the attack. The exploitability is said to be difficult. The exploit has been made public and could be used. Upgrading to version 7.21 will fix this issue. The patch is named 0d882f1b43ff2308b7486a56a9d60cd6dba8a3f1. You should upgrade the affected component. The vendor was contacted early, responded in a very professional manner and quickly released a fixed version of the affected product.

A vulnerability has been found in Cesanta Mongoose up to 7.20. This affects the function mgtlsrecvcert of the file mongoose.c of the component TLS 1.3 Handler. Such manipulation of the argument pubkey leads to heap-based buffer overflow. The attack may be launched remotely. The exploit has been disclosed to the public and may be used. Upgrading to version 7.21 mitigates this issue. The name of the patch is 0d882f1b43ff2308b7486a56a9d60cd6dba8a3f1. It is advisable to upgrade the affected component. The vendor was contacted early, responded in a very professional manner and quickly released a fixed version of the affected product.

A vulnerability was detected in Cesanta Mongoose up to 7.20. This impacts the function mgchacha20poly1305decrypt of the file /src/tlschacha20.c of the component Poly1305 Authentication Tag Handler. The manipulation results in improper verification of cryptographic signature. The attack may be launched remotely. This attack is characterized by high complexity. The exploitability is said to be difficult. The exploit is now public and may be used. The vendor was contacted early about this disclosure but did not respond in any way.

A security vulnerability has been detected in Cesanta Mongoose up to 7.20. This affects the function getpeer of the file /src/netbuiltin.c of the component TCP Sequence Number Handler. The manipulation leads to improper verification of source of a communication channel. The attack may be initiated remotely. The attack's complexity is rated as high. The exploitability is reported as difficult. The exploit has been disclosed publicly and may be used. The vendor was contacted early about this disclosure but did not respond in any way.

A weakness has been identified in Cesanta Mongoose up to 7.20. The impacted element is the function mgsendnsreq of the file /src/dns.c of the component DNS Transaction ID Handler. Executing a manipulation of the argument random can lead to insufficiently random values. The attack can be launched remotely. The attack requires a high level of complexity. The exploitability is regarded as difficult. The exploit has been made available to the public and could be used for attacks. The vendor was contacted early about this disclosure but did not respond in any way.

Null pointer dereference in addcacerts() in Cesanta Mongoose before 7.2 allows remote attackers to cause a denial of service via TLS initialization where SSLCTXgetcertstore() returns NULL.

Improper Neutralization of Delimiters vulnerability in Cesanta Mongoose Web Server v7.14 allows to trigger an infinite loop bug if the input string contains unexpected characters.

Use of Out-of-range Pointer Offset vulnerability in Cesanta Mongoose Web Server v7.14 allows an attacker to send an unexpected TLS packet and force the application to read unintended heap memory space.

Use of Out-of-range Pointer Offset vulnerability in Cesanta Mongoose Web Server v7.14 allows an attacker to send an unexpected TLS packet and produce a segmentation fault on the application.

Improper Neutralization of Delimiters vulnerability in Cesanta Mongoose Web Server v7.14 allows to trigger an out-of-bound memory write if the PEM certificate contains unexpected characters.

Integer Overflow or Wraparound vulnerability in Cesanta Mongoose Web Server v7.14 allows an attacker to send an unexpected TLS packet and produce a segmentation fault on the application.

Cesanta Mongoose commit b316989 was discovered to contain a NULL pointer dereference via the scpy function at src/fmt.c. This vulnerability allows attackers to cause a Denial of Service (DoS) via a crafted MQTT packet.

The HTTP server in Mongoose before 7.10 accepts requests containing negative Content-Length headers. By sending a single attack payload over TCP, an attacker can cause an infinite loop in which the server continuously reparses that payload, and does not respond to any other requests.

This affects the package cesanta/mongoose before 7.6. The unsafe handling of file names during upload using mghttpupload() method may enable attackers to write files to arbitrary locations outside the designated target folder.