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.

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.

Use-after-free vulnerability in the mgcgievhandler function in mongoose.c in Cesanta Mongoose Embedded Web Server Library 6.13 and earlier allows a denial of service (application crash) or remote code execution.

An exploitable memory corruption vulnerability exists in the Websocket protocol implementation of Cesanta Mongoose 6.8. A specially crafted websocket packet can cause an integer overflow, leading to a heap buffer overflow and resulting in denial of service and potential remote code execution. An attacker needs to send a specially crafted websocket packet over network to trigger this vulnerability.

An exploitable memory corruption vulnerability exists in the Websocket protocol implementation of Cesanta Mongoose 6.8. A specially crafted websocket packet can cause a buffer to be allocated while leaving stale pointers which leads to a use-after-free vulnerability which can be exploited to achieve remote code execution. An attacker needs to send a specially crafted websocket packet over the network to trigger this vulnerability.

An infinite loop programming error exists in the DNS server functionality of Cesanta Mongoose 6.8 library. A specially crafted DNS request can cause an infinite loop resulting in high CPU usage and Denial Of Service. An attacker can send a packet over the network to trigger this vulnerability.

Cross-site request forgery (CSRF) vulnerability in Mongoose Web Server before 6.9 allows remote attackers to hijack the authentication of users for requests that modify Mongoose.conf via a request to mgadmin?save. NOTE: this issue can be leveraged to execute arbitrary code remotely.

Directory traversal vulnerability in Mongoose 2.4 allows remote attackers to read arbitrary files via a .. (dot dot) in the URI.