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Netty CVE-2026-55831

HIGH
Allocation of Resources Without Limits or Throttling (CWE-770)
2026-07-20 GitHub_M GHSA-6jqx-86gh-f27w
Denial Of Service Red Hat Suse Netty
7.5
CVSS 3.1 · Vendor: GitHub_M
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Severity by source

Vendor (GitHub_M) PRIMARY
7.5 HIGH
AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H
vuln.today AI
7.5 HIGH

Single unauthenticated network frame triggers unbounded allocation with availability-only impact; requires SPDY handler enabled but no privileges, so PR:N and A:H.

3.1 AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H
4.0 AV:N/AC:L/AT:N/PR:N/UI:N/VC:N/VI:N/VA:H/SC:N/SI:N/SA:N
SUSE
HIGH
qualitative
Red Hat
7.5 HIGH
qualitative

Primary rating from Vendor (GitHub_M).

CVSS VectorVendor: GitHub_M

Attack Vector
Network
Attack Complexity
Low
Privileges Required
None
User Interaction
None
Scope
Unchanged
Confidentiality
None
Integrity
None
Availability
High

Lifecycle Timeline

3
Source Code Evidence Fetched
Jul 20, 2026 - 23:45 vuln.today
Analysis Generated
Jul 20, 2026 - 23:45 vuln.today
CVE Published
Jul 20, 2026 - 23:00 cve.org
HIGH 7.5

Blast Radius

ecosystem impact
† from your stack dependencies † transitive graph · vuln.today resolves 4-path depth
  • 344 maven packages depend on io.netty:netty-codec-http (32 direct, 312 indirect)

Ecosystem-wide dependent count for version 4.2.0.Final.

DescriptionCVE.org

Netty is a network application framework for development of protocol servers and clients. Prior to 4.1.136.Final and 4.2.16.Final, Netty's SPDY SETTINGS decoder accepts a peer-declared SETTINGS entry count up to the 24-bit frame-length limit and materializes every unique setting ID in DefaultSpdySettingsFrame, allowing a remote SPDY/3.1 peer to send a syntactically valid roughly 2 MiB SETTINGS frame that creates 262144 map entries and amplifies network input into heap growth and ordered-map insertion work. This issue is fixed in versions 4.1.136.Final and 4.2.16.Final.

AnalysisAI

Memory-amplification denial of service in the Netty network framework (SPDY/3.1 codec) prior to 4.1.136.Final and 4.2.16.Final allows a remote unauthenticated peer to send a single ~2 MiB SPDY SETTINGS frame that forces the server to materialize 262,144 map entries in DefaultSpdySettingsFrame, driving heap growth and ordered-map insertion CPU cost far out of proportion to the input. Affected are Java services that enable Netty's SPDY handler and accept untrusted connections; there is no public exploit identified at time of analysis, and while CVSS is 7.5 the low EPSS-style real-world footprint is tempered by SPDY/3.1 being a deprecated, rarely-enabled protocol.

Technical ContextAI

Netty is a widely used asynchronous event-driven network application framework for the JVM, providing codecs for numerous protocols including the now-deprecated SPDY/3.1. The flaw sits in the SPDY SETTINGS frame decoder: the SETTINGS frame carries a peer-declared entry count, and Netty trusted that count up to the 24-bit frame-length ceiling without validating it against the bytes actually available or a sane upper bound. Each declared unique setting ID is inserted into the ordered map backing DefaultSpdySettingsFrame, so a compact wire frame expands into hundreds of thousands of Java objects and map insertions. This is a textbook CWE-770 (Allocation of Resources Without Limits or Throttling) issue where attacker-controlled input directly governs allocation volume without a bound.

RemediationAI

Vendor-released patch: upgrade to Netty 4.1.136.Final or 4.2.16.Final, which bound the accepted SETTINGS entry count so an oversized frame is rejected rather than materialized. As a compensating control where immediate upgrade is not possible, disable the SPDY/3.1 handler and migrate clients to HTTP/2, since SPDY is deprecated - this removes the vulnerable code path entirely with the trade-off of dropping legacy SPDY client support. If SPDY must remain enabled, front the service with a reverse proxy or WAF that caps SPDY frame sizes or terminates SPDY, and constrain per-connection memory and enforce connection rate/size limits to blunt amplification, accepting the operational cost of the added tier. Refer to the advisory at https://github.com/netty/netty/security/advisories/GHSA-6jqx-86gh-f27w for authoritative guidance.

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Vendor StatusVendor

SUSE

Severity: Important
Product Status
SUSE Linux Enterprise Desktop 15 SP7 Not-Affected
SUSE Linux Enterprise Desktop 15 SP7 Not-Affected
SUSE Linux Enterprise High Performance Computing 15 SP7 Not-Affected
SUSE Linux Enterprise High Performance Computing 15 SP7 Not-Affected
SUSE Linux Enterprise Module for Development Tools 15 SP7 Not-Affected

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CVE-2026-55831 vulnerability details – vuln.today
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