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High, CVSS 7.5amended

Excessive Iteration in gRPC

CVE-2023-33953GHSA-496j-2rq6-j6cc

What to do

Vendor fix available. Upgrade each affected package to the fixed version on its release line (grpc 1.56.2, 1.55.2, 1.54.3, 1.53.2; grpcio 1.56.2, 1.55.2, 1.54.3, 1.53.2), redeploy, then verify what is actually installed.

This page has no inventory attached, so it cannot say whether you are affected. A vendor fix is not proof that your deployment is fixed.

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Affected packages

  • RubyGems grpc

    Affected
    < 1.53.2>= 1.54.0, < 1.54.3>= 1.55.0, < 1.55.2>= 1.56.0, < 1.56.2
    Fixed in
    1.54.3, 1.55.2, 1.53.2, 1.56.2

  • PyPI grpcio

    Affected
    < 1.53.2>= 1.54.0, < 1.54.3>= 1.55.0, < 1.55.2>= 1.56.0, < 1.56.2
    Fixed in
    1.54.3, 1.55.2, 1.53.2, 1.56.2

Sources

Severity and exploitation
Exploitation
No confirmed exploitation recorded. Patch Next marks exploitation only from CISA KEV.
CVSS
7.5 · CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H
EPSS
  • CVE-2023-33953: 0.48% estimated exploitation activity in the next 30 days; percentile 41.40 (FIRST EPSS, 2026-11-03). This is a model estimate, not proof of exploitation or customer exposure.
Source description

As published by the source; long descriptions are shortened.

gRPC contains a vulnerability that allows hpack table accounting errors could lead to unwanted disconnects between clients and servers in exceptional cases/ Three vectors were found that allow the following DOS attacks: - Unbounded memory buffering in the HPACK parser - Unbounded CPU consumption in the HPACK parser The unbounded CPU consumption is down to a copy that occurred per-input-block in the parser, and because that could be unbounded due to the memory copy bug we end up with an O(n^2) parsing loop, with n selected by the client. The unbounded memory buffering bugs: - The header size limit check was behind the string reading code, so we needed to first buffer up to a 4 gigabyte string before rejecting it as longer than 8 or 16kb. - HPACK varints have an encoding quirk whereby an infinite number of 0’s can be added at the start of an integer. gRPC’s hpack parser needed to read all of them before concluding a parse. - gRPC’s metadata overflow check was performed per frame, so…

Dates and revisions
Published by the source
Last modified by the source
Source last checked
  1. Revision 2 · amended ·

    Amended from ghsa record GHSA-496j-2rq6-j6cc

  2. Revision 1 · created ·

    Published from osv record GHSA-496j-2rq6-j6cc

Agent brief

Preview the exact text before you copy it. Commands are read-only suggestions; review them before running anything.

# Patch Next advisory brief: CVE-2023-33953

Advisory: Excessive Iteration in gRPC
IDs: CVE-2023-33953, GHSA-496j-2rq6-j6cc
Record: https://patchnext.com/advisories/cve-2023-33953 (revision 2, source checked 26 Oct 2026, 13:16 UTC)
Inventory: none attached. This brief comes from a public page and does not say whether any deployment is affected.
Severity: High (CVSS 7.5)
Exploitation: no confirmed exploitation recorded. Patch Next confirms exploitation only from CISA KEV.
Vendor response: Vendor fix available; fixed versions by package: grpc 1.56.2, 1.55.2, 1.54.3, 1.53.2; grpcio 1.56.2, 1.55.2, 1.54.3, 1.53.2. A vendor fix does not mean a deployment is fixed.

## Affected components
- RubyGems grpc: affected < 1.53.2; >= 1.54.0, < 1.54.3; >= 1.55.0, < 1.55.2; >= 1.56.0, < 1.56.2; fixed in 1.54.3, 1.55.2, 1.53.2, 1.56.2
- PyPI grpcio: affected < 1.53.2; >= 1.54.0, < 1.54.3; >= 1.55.0, < 1.55.2; >= 1.56.0, < 1.56.2; fixed in 1.54.3, 1.55.2, 1.53.2, 1.56.2

## Suggested inspection (read-only)
- RubyGems grpc: check the installed version with your package manager.
- `python -m pip show grpcio`: prints the installed version. Run with the environment that serves production active.

## Supported action
Upgrade each affected component to a fixed version on its release line. For a transitive dependency, upgrade the parent package or add an override or constraint, then regenerate the lockfile. Redeploy every environment that ran an affected version.

## Required regression checks
- Run the test suite and a production build.
- Exercise the features that depend on grpc, grpcio.
- Repeat the inspection and confirm that only fixed versions remain installed.

## Rollback considerations
- Keep the previous lockfile and deployment artifact. Rolling back reinstates the vulnerable version, so apply any documented mitigation while you fix forward.

## Unresolved questions
- Which deployments run an affected version?
- Exploitation status can change. Check again before lowering the priority.
- Mark the work resolved only after the fixed version is verified in production.

## Sources
- Verified: https://osv.dev/vulnerability/GHSA-496j-2rq6-j6cc (OSV record GHSA-496j-2rq6-j6cc lists affected ranges: PyPI grpcio >=0 =1.54.0 =1.55.0 =1.56.0 =0 =1.54.0 =1.55.0 =1.56.0 <1.56.2 (fixed))
- Verified: https://github.com/advisories/GHSA-496j-2rq6-j6cc (GitHub-reviewed advisory GHSA-496j-2rq6-j6cc lists affected ranges: PyPI grpcio >=0 =1.54.0 =1.55.0 =1.56.0 =0 =1.54.0 =1.55.0 =1.56.0 <1.56.2)

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