Vulnerability in io.netty:netty-handler (CVE-2026-75595)
Summary
Vulnerability in io.netty:netty-handler (CVE-2026-75595). Confidential information can be exposed externally. Exploitable via SslContext. Mitigation: upgrade to 4.1.137.Final or later.
Original description
The description as published by the source.
Summary
A fragmented TLS ClientHello whose handshake header spans multiple records makes Netty silently fall back to the default SslContext; where per-SNI selection is the sole mTLS gate, an unauthenticated attacker can bypass the route's mTLS requirement.
Details
In io.netty.handler.ssl.SslClientHelloHandler#decode the guard that should wait for the 4-byte handshake header checks the wrong offset - it ignores the 5-byte record header that precedes it - and therefore never fires:
if (handshakeLength == -1) {
if (readerIndex + 4 > endOffset) {
// Need more data to read HandshakeType and handshakeLength (4 bytes)
return;
}
When the first record's payload is < 4 bytes, handshakeLength = in.getUnsignedMedium(readerIndex + SslUtils.SSL_RECORD_HEADER_LENGTH + 1); leads to IndexOutOfBoundsException . That is caught by the generic catch (Exception) block, which calls select(ctx, null) - this is the default SslContext. Fallback to default on parse failure is a problem when per-SNI selection is the sole mTLS gate.
Impact
SNI routing bypass. Escalates to an unauthenticated mTLS bypass only when:
- mTLS is enforced solely via per-SNI SslContext (clientAuth=REQUIRE)
- the default/fallback SslContext is permissive (clientAuth=NONE/OPTIONAL)
- no secondary peer-certificate verification exists at the application layer.
Source: NIST National Vulnerability Database NVD GitHub Advisory
Auto-generated summary
Assembled by SecPulse from the source data (CVSS, CWE, affected versions) using templates — no AI involved. Check the original description and references below for exact details.
A vulnerability tracked as CVE-2026-75595 has been found in io.netty:netty-handler.
Attackers can target a specific entry point like SslContext over the network to misuse the product.
Confidential information can be exposed externally. CVSS score: 9.1/10.
What to do: upgrade io.netty:netty-handler to 4.1.137.Final or later.
If unsure, ask your IT team or search "io.netty:netty-handler CVE-2026-75595" on the vendor's site.
CVE-2026-75595 (io.netty:netty-handler) — CWE-475 / CVSS v3 9.1
Attack vector: remote (network-reachable) / unauthenticated / no user interaction
Attack surface: SslContext
Patched: 4.1.137.Final — apply immediately
Plan: 1) Audit SBOM/dependencies, 2) Stage→prod upgrade, 3) Add WAF/proxy monitoring on affected endpoints, 4) Hunt IOCs in logs.
Refs: see the GHSA / vendor advisory / patched release linked on this page.
A vulnerability (CWE-475) exists in io.netty:netty-handler. Attackers reach the vulnerable code path via SslContext without authentication.
Check the vendor advisory for the affected versions of io.netty:netty-handler. Attack surface: SslContext.
Severity: Critical (CVSS 9.1/10). Confidential information can be exposed externally.
Update to 4.1.137.Final.
Until the patch is applied: disable the affected feature, apply WAF rules, or restrict access via network ACLs.
Search webserver/proxy logs for unusual request patterns matching this CVE's known IOCs. Audit SBOM/dependencies to find affected services.
Response actions
Concrete steps and command examples for SOC/SRE teams to execute in order
-
1Identify exposure identify
Audit SBOM/dependencies for affected components.資産台帳・SBOM・依存マニフェストで io.netty:netty-handler を使っているサービスとバージョンを洗い出す。
-
2Apply patch patch
Upgrade io.netty:netty-handler to 4.1.137.Finalステージング環境で 4.1.137.Final に上げて回帰テスト → 本番反映。回帰テストはアプリの主要ハッピーパスを含めること。
-
3Post-deployment verification verify
Confirm patched version is live in productionパッチ適用後、ステージングで PoC または同等の悪用パターンを再現して脆弱性が閉じたことを確認。本番ではアクセスログ・WAF でアラート再発が無いか継続監視。
Affected packages
References
- advisory nvd.nist.gov
- ATLASSIAN BAM-26535
- package github.com
- web github.com
- web github.com
- web github.com
- web github.com
- web github.com
- web github.com
- web github.com
- web github.com