CVE-2022-29240: Use of Uninitialized Resource (CWE-908)
value: Scylla is a real-time big data database that is API-compatible with Apache Cassandra and Amazon DynamoDB. When decompressing CQL frame received from user, Scylla assumes that user-provided uncompressed length is correct. If user provides fake length, that is greater than the real one, part of decompression buffer won't be overwritten, and will be left uninitialized. This can be exploited in several ways, depending on the privileges of the user. 1. The main exploit is that an attacker with access to CQL port, but no user account, can bypass authentication, but only if there are other legitimate clients making connections to the cluster, and they use LZ4. 2. Attacker that already has a user account on the cluster can read parts of uninitialized memory, which can contain things like passwords of other users or fragments of other queries / results, which leads to authorization bypass and sensitive information disclosure. The bug has been patched in the following versions: Scylla Enterprise: 2020.1.14, 2021.1.12, 2022.1.0. Scylla Open Source: 4.6.7, 5.0.3. Users unable to upgrade should make sure none of their drivers connect to cluster using LZ4 compression, and that Scylla CQL port is behind firewall. Additionally make sure no untrusted client can connect to Scylla, by setting up authentication and applying workarounds from previous point (firewall, no lz4 compression).
CWE description: The product uses or accesses a resource that has not been initialized.
CVSS v3 base score: 8.1
Published: 2022-09-15T22:15Z
Repository: https://github.com/scylladb/scylladb
Language: C++
Files changed: transport/server.cc
Commit date: 2022-09-07 10:58:23 +0300
Commit message: transport/server.cc: Return correct size of decompressed lz4 buffer

An incorrect size is returned from the function, which could lead to
crashes or undefined behavior. Fix by erroring out in these cases.

Fixes #11476

Diff: diff --git a/transport/server.cc b/transport/server.cc
index e9edff9e4..3e7b1520c 100644
--- a/transport/server.cc
+++ b/transport/server.cc
@@ -725,11 +725,14 @@ future<fragmented_temporary_buffer> cql_server::connection::read_and_decompress_
                     auto ret = LZ4_decompress_safe(reinterpret_cast<const char*>(in.data()), reinterpret_cast<char*>(out.data()),
                                                    in.size(), out.size());
                     if (ret < 0) {
                         throw std::runtime_error("CQL frame LZ4 uncompression failure");
                     }
-                    return out.size();
+                    if (ret != out.size()) {
+                        throw std::runtime_error("Malformed CQL frame - provided uncompressed size different than real uncompressed size");
+                    }
+                    return static_cast<size_t>(ret);
                 });
                 on_compression_buffer_use();
                 return uncomp;
             });
         } else if (_compression == cql_compression::snappy) {

Vulnerable code:                     return out.size();
Fixed code:                     if (ret != out.size()) {
                        throw std::runtime_error("Malformed CQL frame - provided uncompressed size different than real uncompressed size");
                    }
                    return static_cast<size_t>(ret);