CVE-2026-75595
Description
A flaw was found in Netty, an asynchronous, event-driven network application framework. An unauthenticated remote attacker can exploit fragmented Transport Layer Security (TLS) ClientHello messages to bypass the Server Name Indication (SNI) routing mechanism. This forces a fallback to a less secure default SslContext, allowing the attacker to bypass mutual TLS authentication requirements and gain unauthorized access to protected resources.
Statement
This is an Important flaw in Netty that allows an unauthenticated remote attacker to bypass mutual TLS authentication. Applications that use Netty and rely solely on SNI-based clientAuth=REQUIRE for access control, without additional application-layer certificate verification, are vulnerable when an attacker exploits fragmented TLS ClientHello messages to force a fallback to a less secure default SslContext. Deployments that enforce clientAuth=REQUIRE uniformly across all SslContexts, or that perform secondary certificate verification at the application layer, are not affected.
Mitigation
To mitigate this issue, ensure that application-layer certificate verification is implemented for services utilizing Netty with mutual TLS. This provides an additional layer of authentication beyond the TLS handshake, preventing unauthorized access even if the SNI routing is bypassed and a less restrictive default SslContext is used.
Common Vulnerability Scoring System (CVSS) Score Details
Info alert:Important note
CVSS scores for open source components depend on vendor-specific factors (e.g. version or build chain). Therefore, Red Hat's score and impact rating can be different from NVD and other vendors. Red Hat remains the authoritative CVE Naming Authority (CNA) source for its products and services (see Red Hat classifications).
CVSS v3 Score Breakdown
| Red Hat | NVD | cve.org | |
|---|---|---|---|
| Base Score | 7.4 | 9.1 | N/A |
| Attack Vector | Network | Network | N/A |
| Attack Complexity | High | Low | N/A |
| Privileges Required | None | None | N/A |
| User Interaction | None | None | N/A |
| Scope | Unchanged | Unchanged | N/A |
| Confidentiality | High | High | N/A |
| Integrity Impact | High | High | N/A |
| Availability Impact | None | None | N/A |
Vector
Red Hat: CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:H/A:N
NVD: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:N
Understanding the Weakness (CWE)
Confidentiality
Technical Impact: Read Memory
If the untrusted pointer is used in a read operation, an attacker might be able to read sensitive portions of memory.
Availability
Technical Impact: DoS: Crash, Exit, or Restart
If the untrusted pointer references a memory location that is not accessible to the program, or points to a location that is "malformed" or larger than expected by a read or write operation, the application may terminate unexpectedly.
Integrity,Confidentiality,Availability
Technical Impact: Execute Unauthorized Code or Commands; Modify Memory
If the untrusted pointer is used in a function call, or points to unexpected data in a write operation, then code execution may be possible.
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