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Connection confusion in gRPC

High severity GitHub Reviewed Published Jul 5, 2023 to the GitHub Advisory Database • Updated Aug 13, 2025

Package

bundler grpc (RubyGems)

Affected versions

>= 1.53.0, < 1.53.1
>= 1.54.0, < 1.54.2

Patched versions

1.53.1
1.54.2
pip grpcio (pip)
>= 1.53.0, < 1.53.1
>= 1.54.0, < 1.54.2
1.53.1
1.54.2
maven io.grpc:grpc-protobuf (Maven)
>= 1.53.0, < 1.53.1
>= 1.54.0, < 1.54.2
1.53.1
1.54.2

Description

When gRPC HTTP2 stack raised a header size exceeded error, it skipped parsing the rest of the HPACK frame. This caused any HPACK table mutations to also be skipped, resulting in a desynchronization of HPACK tables between sender and receiver. If leveraged, say, between a proxy and a backend, this could lead to requests from the proxy being interpreted as containing headers from different proxy clients - leading to an information leak that can be used for privilege escalation or data exfiltration.

References

Published by the National Vulnerability Database Jun 9, 2023
Published to the GitHub Advisory Database Jul 5, 2023
Reviewed Jul 5, 2023
Last updated Aug 13, 2025

Severity

High

CVSS overall score

This score calculates overall vulnerability severity from 0 to 10 and is based on the Common Vulnerability Scoring System (CVSS).
/ 10

CVSS v3 base metrics

Attack vector
Network
Attack complexity
High
Privileges required
None
User interaction
None
Scope
Unchanged
Confidentiality
High
Integrity
None
Availability
High

CVSS v3 base metrics

Attack vector: More severe the more the remote (logically and physically) an attacker can be in order to exploit the vulnerability.
Attack complexity: More severe for the least complex attacks.
Privileges required: More severe if no privileges are required.
User interaction: More severe when no user interaction is required.
Scope: More severe when a scope change occurs, e.g. one vulnerable component impacts resources in components beyond its security scope.
Confidentiality: More severe when loss of data confidentiality is highest, measuring the level of data access available to an unauthorized user.
Integrity: More severe when loss of data integrity is the highest, measuring the consequence of data modification possible by an unauthorized user.
Availability: More severe when the loss of impacted component availability is highest.
CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:N/A:H

EPSS score

Exploit Prediction Scoring System (EPSS)

This score estimates the probability of this vulnerability being exploited within the next 30 days. Data provided by FIRST.
(22nd percentile)

Weaknesses

Expected Behavior Violation

A feature, API, or function does not perform according to its specification. Learn more on MITRE.

CVE ID

CVE-2023-32731

GHSA ID

GHSA-cfgp-2977-2fmm

Source code

No known source code

Credits

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