CVE-2026-59803: Improper Handling of Highly Compressed Data (Data Amplification) in smallnest rpcx
rpcx through 1.9.3, fixed in commit 047aec1, contains a denial-of-service vulnerability in protocol.Message.Decode (protocol/message.go). When a message has the compression flag set, the payload is gzip-decompressed via util.Unzip with no limit on the decompressed output size. The only built-in size guard, protocol.MaxMessageLength, is checked against the compressed on-the-wire frame length, not the decompressed size, so it provides no protection. Because decoding (and decompression) occurs in readRequest before authentication, a single unauthenticated connection can send a small (under 2 MB) gzip-compressed message that expands to gigabytes of heap allocation, leading to out-of-memory conditions and service unavailability.
AI Analysis
Technical Summary
CVE-2026-59803 is a denial-of-service vulnerability in rpcx through version 1.9.3. The issue arises in protocol.Message.Decode where gzip-compressed payloads are decompressed without limits on the decompressed size. The existing size check only validates the compressed frame length, not the decompressed output, allowing a small compressed message (under 2 MB) to expand to gigabytes of memory allocation. This leads to out-of-memory conditions and service denial. The vulnerability is exploitable without authentication since decompression happens before request authentication.
Potential Impact
An unauthenticated attacker can send a specially crafted compressed message that decompresses to a very large size, causing the rpcx service to consume excessive memory and become unavailable. This results in a denial-of-service condition impacting service availability.
Mitigation Recommendations
Patch status is not yet confirmed — check the vendor advisory for current remediation guidance. The vulnerability is fixed in commit 047aec1, so upgrading to a version including this fix is recommended once available. Until then, consider mitigating by limiting message sizes or disabling compression if possible.
CVE-2026-59803: Improper Handling of Highly Compressed Data (Data Amplification) in smallnest rpcx
Description
rpcx through 1.9.3, fixed in commit 047aec1, contains a denial-of-service vulnerability in protocol.Message.Decode (protocol/message.go). When a message has the compression flag set, the payload is gzip-decompressed via util.Unzip with no limit on the decompressed output size. The only built-in size guard, protocol.MaxMessageLength, is checked against the compressed on-the-wire frame length, not the decompressed size, so it provides no protection. Because decoding (and decompression) occurs in readRequest before authentication, a single unauthenticated connection can send a small (under 2 MB) gzip-compressed message that expands to gigabytes of heap allocation, leading to out-of-memory conditions and service unavailability.
CVSS v4.0
Score 8.7high
Affected software
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AI-Powered Analysis
Machine-generated threat intelligence
Technical Analysis
CVE-2026-59803 is a denial-of-service vulnerability in rpcx through version 1.9.3. The issue arises in protocol.Message.Decode where gzip-compressed payloads are decompressed without limits on the decompressed size. The existing size check only validates the compressed frame length, not the decompressed output, allowing a small compressed message (under 2 MB) to expand to gigabytes of memory allocation. This leads to out-of-memory conditions and service denial. The vulnerability is exploitable without authentication since decompression happens before request authentication.
Potential Impact
An unauthenticated attacker can send a specially crafted compressed message that decompresses to a very large size, causing the rpcx service to consume excessive memory and become unavailable. This results in a denial-of-service condition impacting service availability.
Mitigation Recommendations
Patch status is not yet confirmed — check the vendor advisory for current remediation guidance. The vulnerability is fixed in commit 047aec1, so upgrading to a version including this fix is recommended once available. Until then, consider mitigating by limiting message sizes or disabling compression if possible.
Technical Details
- Data Version
- 5.2
- Assigner Short Name
- VulnCheck
- Date Reserved
- 2026-07-07T14:39:14.062Z
- Cvss Version
- 4.0
- State
- PUBLISHED
- Remediation Level
- null
Threat ID: 6a4ea886c9d9e3dbe3a52527
Added to database: 07/08/2026, 19:44:06 UTC
Last enriched: 07/16/2026, 10:13:46 UTC
Last updated: 08/22/2026, 10:52:10 UTC
Views: 45
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