GHSA-fccg-mwvh-qqg4

Source

https://github.com/advisories/GHSA-fccg-mwvh-qqg4

Import Source

https://github.com/github/advisory-database/blob/main/advisories/github-reviewed/2026/09/GHSA-fccg-mwvh-qqg4/GHSA-fccg-mwvh-qqg4.json

JSON Data

https://api.test.osv.dev/v1/vulns/GHSA-fccg-mwvh-qqg4

Aliases

CVE-2026-75596

Downstream

CGA (1098)

MINI (97)

Published

2026-09-08T18:14:56Z

Modified

2026-09-08T18:28:35Z

Severity

6.9 (Medium) CVSS_V4 - CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:N/VI:N/VA:L/SC:N/SI:N/SA:N CVSS Calculator

Summary

Netty: Fragmented ClientHello records trigger quadratic pre-handshake reassembly in default SNI parsing

Details

Summary

Netty's default SNI entrypoint reparses and recopies previously received ClientHello fragments on every additional TLS handshake record. A remote peer can send a small first record that advertises a large ClientHello length and then drip the body in many tiny records, causing superlinear (quadratic) CPU work before the handshake completes. With 4095 one-byte fragments, the handler recopies 8,386,560 bytes from only 24,579 bytes on the wire — a 341× amplification ratio.

Affected Entrypoints

io.netty.handler.ssl.SniHandler — default constructors
io.netty.handler.ssl.SslClientHelloHandler — pre-handshake ClientHello aggregation path

Vulnerable Code Locations

handler/src/main/java/io/netty/handler/ssl/SniHandler.java:85
handler/src/main/java/io/netty/handler/ssl/SslClientHelloHandler.java:75 (decode entry)
handler/src/main/java/io/netty/handler/ssl/SslClientHelloHandler.java:165 (handshakeBuffer.clear)
handler/src/main/java/io/netty/handler/ssl/SslClientHelloHandler.java:174 (writeBytes re-copy)
codec-base/src/main/java/io/netty/handler/codec/ByteToMessageDecoder.java:294 (cumulation retention)

Exploit Path

1. TCP connection → SniHandler → SslClientHelloHandler.decode
2. First record: TLS handshake header declaring large ClientHello length (e.g., 4096 bytes)
3. Attacker sends thousands of tiny follow-on handshake records (1 byte each)
4. On each fragment: handshakeBuffer.clear() + writeBytes() re-copies ALL accumulated body bytes
5. Total bytes copied = n*(n+1)/2 where n = number of body bytes → quadratic
6. Event-loop CPU exhausted before SslHandler takes over

Impact

Vulnerability Type: Inefficient Algorithmic Complexity
An unauthenticated network attacker can drive disproportionate CPU consumption on the Netty event loop
Affects all Netty deployments using SniHandler for TLS termination (the default SNI path)
No privileges, user interaction, or special configuration required
Can degrade or stall TLS connection handling for all clients on the affected event loop
The attack requires only modest bandwidth (~25 KB) to trigger significant CPU work

Credits

Found by a security research team from the University of Sydney, focusing on detecting open source software vulnerabilities. Liyi Zhou: https://lzhou1110.github.io/ Ziyue Wang: https://zyy0530.github.io/ Strick: https://str1ckl4nd.github.io/ Maurice: https://maurice.busystar.org/ Chenchen Yu: https://7thparkk.github.io/

Database specific

{
    "cwe_ids": [
        "CWE-407"
    ],
    "github_reviewed": true,
    "github_reviewed_at": "2026-09-08T18:14:56Z",
    "nvd_published_at": "2026-08-19T21:17:37Z",
    "severity": "MODERATE"
}

References

Affected packages

Maven / io.netty:netty-handler

Package

Name: io.netty:netty-handler; View open source insights on deps.dev
Purl: pkg:maven/io.netty/netty-handler

Affected ranges

Type: ECOSYSTEM
Events: Introduced

4.2.0.Final

Fixed

4.2.17.Final

Affected versions

4.*

4.2.0.Final

4.2.1.Final

4.2.2.Final

4.2.3.Final

4.2.4.Final

4.2.5.Final

4.2.6.Final

4.2.7.Final

4.2.8.Final

4.2.9.Final

4.2.10.Final

4.2.11.Final

4.2.12.Final

4.2.13.Final

4.2.14.Final

4.2.15.Final

4.2.16.Final

Database specific

last_known_affected_version_range

"<= 4.2.16.Final"

source

"https://github.com/github/advisory-database/blob/main/advisories/github-reviewed/2026/09/GHSA-fccg-mwvh-qqg4/GHSA-fccg-mwvh-qqg4.json"

Maven / io.netty:netty-handler

Package

Name: io.netty:netty-handler; View open source insights on deps.dev
Purl: pkg:maven/io.netty/netty-handler

Affected ranges

Type: ECOSYSTEM
Events: Introduced

0 Unknown introduced version / All previous versions are affected

Fixed

4.1.137.Final

Affected versions

4.*

4.0.0.Alpha1

4.0.0.Alpha2

4.0.0.Alpha3

4.0.0.Alpha4

4.0.0.Alpha5

4.0.0.Alpha6

4.0.0.Alpha7

4.0.0.Alpha8

4.0.0.Beta1

4.0.0.Beta2

4.0.0.Beta3

4.0.0.CR1

4.0.0.CR2

4.0.0.CR3

4.0.0.CR4

4.0.0.CR5

4.0.0.CR6

4.0.0.CR7

4.0.0.CR8

4.0.0.CR9

4.0.0.Final

4.0.1.Final

4.0.2.Final

4.0.3.Final

4.0.4.Final

4.0.5.Final

4.0.6.Final

4.0.7.Final

4.0.8.Final

4.0.9.Final

4.0.10.Final

4.0.11.Final

4.0.12.Final

4.0.13.Final

4.0.14.Beta1

4.0.14.Final

4.0.15.Final

4.0.16.Final

4.0.17.Final

4.0.18.Final

4.0.19.Final

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4.0.56.Final

4.1.0.Beta1

4.1.0.Beta2

4.1.0.Beta3

4.1.0.Beta4

4.1.0.Beta5

4.1.0.Beta6

4.1.0.Beta7

4.1.0.Beta8

4.1.0.CR1

4.1.0.CR2

4.1.0.CR3

4.1.0.CR4

4.1.0.CR5

4.1.0.CR6

4.1.0.CR7

4.1.0.Final

4.1.1.Final

4.1.2.Final

4.1.3.Final

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4.1.132.Final

4.1.133.Final

4.1.134.Final

4.1.135.Final

4.1.136.Final

Database specific

last_known_affected_version_range

"<= 4.1.136.Final"

source

"https://github.com/github/advisory-database/blob/main/advisories/github-reviewed/2026/09/GHSA-fccg-mwvh-qqg4/GHSA-fccg-mwvh-qqg4.json"