CVE-2026-75595
CriticalCVSS 9.1Exploitation Probability (EPSS)
Low risk21th percentile - higher than 21% of all known CVEs
Summary
Netty is an asynchronous, event-driven network application framework. Prior to 4.1.137.Final and 4.2.17.Final, io.netty.handler.ssl.SslClientHelloHandler#decode checks the wrong offset before reading the four-byte TLS handshake header, so a ClientHello whose handshake header spans records can cause an IndexOutOfBoundsException and invoke select(ctx, null). This selects the default SslContext instead of the SNI-specific context. In deployments where per-SNI clientAuth=REQUIRE is the sole mutual TLS gate, the default SslContext uses clientAuth=NONE or clientAuth=OPTIONAL, and no application-layer certificate verification exists, an unauthenticated remote attacker can bypass the protected route's mutual TLS requirement. This issue is fixed in versions 4.1.137.Final and 4.2.17.Final.
Risk Assessment
A remote attacker can bypass mutual TLS authentication and gain access to protected resources, potentially leading to unauthorized access and security compromise.
Recommendation
Update Netty to version 4.1.137.Final or 4.2.17.Final (or later) to fix the vulnerability.
Other vulnerabilities in Netty
See all- CVE-2026-42583High
Netty prior to versions 4.2.13.Final and 4.1.133.Final has a vulnerability in Lz4FrameDecoder that allocates a ByteBuf of size decompressedLength, potentially leading to uncontrolled memory allocation. An attacker can exploit a 21-byte header and compressed data to force this allocation.
- CVE-2026-42577High
Netty, an asynchronous network application framework, has an issue in versions from 4.2.0.Final to 4.2.13.Final where the epoll transport fails to detect and close TCP connections that receive a RST after being half-closed. This leads to stale channels that are never cleaned up and, in some code paths, a 100% CPU busy-loop in the event loop thread.
- CVE-2016-4970High
In Netty versions 4.0.x before 4.0.37.Final and 4.1.x before 4.1.1.Final, a vulnerability in OpenSslEngine.java allows remote attackers to cause a denial of service (infinite loop).
- CVE-2026-56817Critical
Netty versions 4.2.0.Final through 4.2.15.Final and 4.1.0.Final through 4.1.135.Final have a vulnerability in XmlDecoder where delivering XML with a DOCTYPE declaration to an AsyncXMLInputFactory without security configuration can activate DTD and entity handling, creating XML External Entity (XXE) risk.
- CVE-2026-100666High
Netty HttpServerCodec up to 4.2.17.Final and 4.1.137.Final incorrectly pairs responses with requests when HTTP/1.1 pipelining with Expect: 100-continue is used, leading to response splitting and unsafe connection reuse.
- CVE-2026-100665High
Netty from 4.2.11.Final before 4.2.18.Final has an incomplete hostname verification fix in the QUIC certificate path when using a plain X509TrustManager, allowing attackers to present a certificate for the wrong hostname.
- CVE-2026-100664High
Netty's HTTP/3 codec from 4.2.2.Final through 4.2.17.Final builds the :authority pseudo-header from the Host header before considering the authority of an absolute-form request-target, leading to authority confusion.
- CVE-2026-100663High
Netty's HTTP/3 codec from 4.2.2.Final through 4.2.17.Final does not special-case HTTP/1 CONNECT authority-form request-targets, resulting in malformed HTTP/3 CONNECT with attacker-controlled authority.
- CVE-2026-100662High
Netty's HTTP/3 codec from 4.2.0.Final through 4.2.17.Final has an uncontrolled resource consumption vulnerability in the QPACK encoder-stream instruction decoder, allowing an attacker to declare huge literal lengths, causing unbounded heap growth and OutOfMemoryError.
- CVE-2026-100661High
Netty's QPACK prefixed-integer decoder (netty-codec-http3) from 4.2.0.Final through 4.2.17.Final does not bound continuation bytes, allowing an attacker to cause O(N^2) CPU cost and memory growth, leading to OOM and event-loop starvation.
Original NVD description (English source)
Netty is an asynchronous, event-driven network application framework. Prior to 4.1.137.Fina and 4.2.17.Final, io.netty.handler.ssl.SslClientHelloHandler#decode checks the wrong offset before reading the four-byte TLS handshake header, so a ClientHello whose handshake header spans records can cause an IndexOutOfBoundsException and invoke select(ctx, null). This selects the default SslContext instead of the SNI-specific context. In deployments where per-SNI clientAuth=REQUIRE is the sole mutual TLS gate, the default SslContext uses clientAuth=NONE or clientAuth=OPTIONAL, and no application-layer certificate verification exists, an unauthenticated remote attacker can bypass the protected route's mutual TLS requirement. This issue is fixed in versions 4.1.137.Final and 4.2.17.Final.
Vulnerability data from NVD (NIST) · CISA KEV · EPSS