PYSEC-2026-1442 H2O Vulnerable to Execution of Arbitrary Files

In h2oai/h2o-3 version 3.46.0, an endpoint exposing a custom EncryptionTool allows an attacker to encrypt any files on the target server with a key of their choosing. The chosen key can also be overwritten, resulting in ransomware-like behavior. This vulnerability makes it possible for an attacke...

H2O Vulnerable to Denial of Service (DoS) via `/3/ParseSetup` Endpoint

A vulnerability in the /3/ParseSetup endpoint of h2oai/h2o-3 version 3.46.0.1 allows for a denial of service DoS attack. The endpoint applies a user-specified regular expression to a user-controllable string. This can be exploited by an attacker to cause inefficient regular expression complexity,...

H2O Vulnerable to Denial of Service (DoS) via `/3/Parse` Endpoint

A vulnerability in the /3/Parse endpoint of h2oai/h2o-3 version 3.46.0.1 allows for a denial of service DoS attack. The endpoint uses a user-specified string to construct a regular expression, which is then applied to another user-specified string. By sending multiple simultaneous requests, an...

H2O Vulnerable to Denial of Service (DoS) and File Write

In h2oai/h2o-3 version 3.46.0.1, the runtool command exposes classes in the water.tools package through the ast parser. This includes the XGBoostLibExtractTool class, which can be exploited to shut down the server and write large files to arbitrary directories, leading to a denial of service...

PYSEC-2026-1444 H2O Vulnerable to Denial of Service (DoS) and File Write

In h2oai/h2o-3 version 3.46.0.1, the runtool command exposes classes in the water.tools package through the ast parser. This includes the XGBoostLibExtractTool class, which can be exploited to shut down the server and write large files to arbitrary directories, leading to a denial of service...

PYSEC-2026-1445 H2O Vulnerable to Denial of Service (DoS) via `/3/Parse` Endpoint

A vulnerability in the /3/Parse endpoint of h2oai/h2o-3 version 3.46.0.1 allows for a denial of service DoS attack. The endpoint uses a user-specified string to construct a regular expression, which is then applied to another user-specified string. By sending multiple simultaneous requests, an...

PYSEC-2026-1437 h2o vulnerable to unexpected POST request shutting down server

In h2oai/h2o-3 version 3.46.0, the runtool command in the rapids component allows the main function of any class under the water.tools namespace to be called. One such class, MojoConvertTool, crashes the server when invoked with an invalid argument, causing a denial of service...

PYSEC-2026-1446 Arbitrary system path lookup in h20

In h2oai/h2o-3 version 3.40.0.4, an exposure of sensitive information vulnerability exists due to an arbitrary system path lookup feature. This vulnerability allows any remote user to view full paths in the entire file system where h2o-3 is hosted. Specifically, the issue resides in the Typeahead...

External Control of File Name or Path in h2oai/h2o-3

Remote unauthenticated attackers can overwrite arbitrary server files with attacker-controllable data. The data that the attacker can control is not entirely arbitrary. h2o writes a CSV/XLS/etc file to disk, so the attacker data is wrapped in quotations and starts with "C1", if they're exporting ...

PYSEC-2026-352 H2O.ai H2O vulnerable to deserialization attacks via a JDBC Connection URL

H2O.ai H2O through 3.46.0.4 allows attackers to arbitrarily set the JDBC URL, leading to deserialization attacks, file reads, and command execution. Exploitation can occur when an attacker has access to post to the ImportSQLTable URI with a JSON document containing a connectionurl property with a...

PYSEC-2026-349 H2O affected by a deserialization vulnerability

A deserialization vulnerability exists in h2oai/h2o-3 versions = 3.46.0.7, allowing attackers to read arbitrary system files and execute arbitrary code. The vulnerability arises from improper handling of JDBC connection parameters, which can be exploited by bypassing regular expression checks and...

PYSEC-2026-351 H2O Deserialization of Untrusted Data Vulnerability

A vulnerability in the h2oai/h2o-3 REST API versions 3.46.0.4 allows unauthenticated remote attackers to execute arbitrary code via deserialization of untrusted data. The vulnerability exists in the endpoints POST /99/ImportSQLTable and POST /3/SaveToHiveTable, where user-controlled JDBC URLs are...

FreeBSD : h2o -- heap overrun parsing zero-length SNI (fba766f4-ccda-4e1b-8875-ab857c6a6532)

The version of FreeBSD installed on the remote host is prior to tested version. It is, therefore, affected by a vulnerability as referenced in the fba766f4-ccda-4e1b-8875-ab857c6a6532 advisory. h2o project reports: When h2o receives a TLS or QUIC ClientHello containing a zero-length SNI extension...

FreeBSD : h2o -- stack overflow serving static files on musl libc (644d5e6c-1bd9-4904-8440-16c04100a2e1)

The version of FreeBSD installed on the remote host is prior to tested version. It is, therefore, affected by a vulnerability as referenced in the 644d5e6c-1bd9-4904-8440-16c04100a2e1 advisory. h2o project reports: When serving static files, h2o can allocate a file path on the stack using alloca...

FreeBSD : h2o -- HTTP/2 state amplification denial of service (35c57495-2231-4733-a66e-044f3dad8b21)

The version of FreeBSD installed on the remote host is prior to tested version. It is, therefore, affected by a vulnerability as referenced in the 35c57495-2231-4733-a66e-044f3dad8b21 advisory. h2o project reports: An HTTP/2 attack can combine HPACK decompression state amplification with stalled...

CVE-2026-3960

A critical remote code execution vulnerability exists in the unauthenticated REST API endpoint /99/ImportSQLTable in H2O-3 version 3.46.0.9 and prior. The vulnerability arises due to insufficient security controls in the parameter blacklist mechanism, which only targets MySQL JDBC driver-specific...

CVE-2026-8750

A vulnerability was identified in h2oai h2o-3 up to 7402. Affected by this issue is the function importFiles of the file h2o-core/src/main/java/water/persist/PersistNFS.java of the component ImportFile API. Such manipulation leads to information disclosure. The attack can be executed remotely. Th...

CVE-2026-8752

A weakness has been identified in h2oai h2o-3 up to 7402. This vulnerability affects the function exec of the file h2o-core/src/main/java/water/rapids/ast/prims/misc/AstSetProperty.java of the component Rapids setproperty Primitive Handler. Executing a manipulation can lead to improper access...

CVE-2026-8751

A security flaw has been discovered in h2oai h2o-3 up to 7402. This affects the function importBinaryModel of the file h2o-core/src/main/java/hex/Model.java of the component JAR Handler. Performing a manipulation results in deserialization. The attack is possible to be carried out remotely. The...

CVE-2026-8752

A weakness has been identified in h2oai h2o-3 up to 7402. This vulnerability affects the function exec of the file h2o-core/src/main/java/water/rapids/ast/prims/misc/AstSetProperty.java of the component Rapids setproperty Primitive Handler. Executing a manipulation can lead to improper access...