CVE-2025-4565

Unbounded recursion in Python Protobuf

MEDIUM

5.3

CVSS Score

Published: June 16, 2025 at 02:50 PM UTC

Updated: June 17, 2026 at 09:33 AM UTC

3 products affected across 2 vendorsProtobuf PythonProtobufProtobuf Python

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Severity

MEDIUM5.3

Exploit prediction

EPSS 0.3%

SSVC

No known exploit

Description

Any project that uses Protobuf Pure-Python backend to parse untrusted Protocol Buffers data containing an arbitrary number of recursive groups, recursive messages or a series of SGROUP tags can be corrupted by exceeding the Python recursion limit. This can result in a Denial of service by crashing the application with a RecursionError. We recommend upgrading to version =>6.31.1 or beyond commit 17838beda2943d08b8a9d4df5b68f5f04f26d901

Affected

Our own answer: ranges merged, affected separated from platform-only, with confidence and review flags.

Protobuf Python · Google

95%

v < 4.25.85.26.0 ≤ v < 5.29.56.30.0 ≤ v < 6.31.1

Affected range stops below 4.25.8, so it looks safe — our inference, not a vendor statement

Affected range stops below 5.29.5, so it looks safe — our inference, not a vendor statement

Affected range stops below 6.31.1, so it looks safe — our inference, not a vendor statement

Protobuf · Protocolbuffers

85%

All versions

Protobuf Python · Protocolbufferspypi

60%

v < 4.25.8v < 5.29.5v < 6.31.1

Affected range stops below 4.25.8, so it looks safe — our inference, not a vendor statement

Affected range stops below 5.29.5, so it looks safe — our inference, not a vendor statement

Affected range stops below 6.31.1, so it looks safe — our inference, not a vendor statement

Remediation

No guide yet

No remediation guidance has been written for this CVE yet. What the record does show:

Patch and advisory references

https://github.com/protocolbuffers/protobuf/commit/17838beda2943d08b8a9d4df5b68f5f04f26d901

References (1)

Patch

Source: [email protected]

https://github.com/protocolbuffers/protobuf/commit/17838beda2943d08b8a9d4df5b68f5f04f26d901

SSVC — Action Prioritization

SSVCNo known exploitAutomatablePartial impact

SSVC signals action urgency (what to patch first), separate from CVSS which measures severity.

CVSS

5.3MEDIUM[email protected]

Attack Vector: NETWORK
Complexity: LOW
Privileges: NONE
User Interaction: NONE
Scope: UNCHANGED
Confidentiality: NONE
Integrity: NONE
Availability: LOW

Vector?

Quick Info

StatusANALYZED

CWE

CWE-674

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