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Packfile parsing exploit

High
coopernetes published GHSA-xxmh-rf63-qwjv Jul 30, 2025

Package

npm @finos/git-proxy (npm)

Affected versions

<=1.19.1

Patched versions

1.19.2, 2.0.0

Description

Summary

An attacker can craft a malicious Git packfile to exploit the PACK signature detection in the parsePush.ts. By embedding a misleading PACK signature within commit content and carefully constructing the packet structure, the attacker can trick the parser into treating invalid or unintended data as the packfile. Potentially, this would allow bypassing approval or hiding commits.

Details

The affected version of parsePush.ts attempts to locate the Git PACK file by looking for the last occurrence of the string "PACK" in the incoming push payload:

const packStart = buffer.lastIndexOf('PACK');

This assumes that any "PACK" string near the end of the push is the beginning of the actual binary Git packfile. However, Git objects (commits, blobs, etc.) can contain arbitrary content (including the word PACK) in binary or non-compressed blobs.

An attacker could abuse this by:

  1. Crafting a custom packfile using low-level Git tools or by manually forging one
  2. Placing the string "PACK" inside a commit body or a binary file blob that appears after the real PACK start in the stream.

The parser then ignores the actual push and treats the binary blob/commit body as the PACK file. The actual push contents may violate existing push policies.

PoC

  1. Make a commit on any branch (example: test-branch) containing the string "PACK"
  2. Manually generate a custom packfile with both branches using git pack-objects or a low-level library/custom script:
    a) Add the string "PACK" after the real packfile's PACK header in the binary stream
  3. Push using a custom client/raw protocol injection

Impact

Attackers with push access can hide commits from scanning/approval and make changes that bypass policies, potentially inserting unwanted/malicious code into a GitProxy protected repository.

The vulnerability impacts all users or organizations relying on GitProxy to enforce policies and prevent unapproved changes. It requires no elevated privileges beyond regular push access, and no extra user interaction, however, it does require a considerable amount of technical skill and intentional effort to accomplish.

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 v4 base metrics

Exploitability Metrics
Attack Vector Network
Attack Complexity High
Attack Requirements None
Privileges Required Low
User interaction None
Vulnerable System Impact Metrics
Confidentiality None
Integrity High
Availability None
Subsequent System Impact Metrics
Confidentiality None
Integrity High
Availability None

CVSS v4 base metrics

Exploitability Metrics
Attack Vector: This metric reflects the context by which vulnerability exploitation is possible. This metric value (and consequently the resulting severity) will be larger the more remote (logically, and physically) an attacker can be in order to exploit the vulnerable system. The assumption is that the number of potential attackers for a vulnerability that could be exploited from across a network is larger than the number of potential attackers that could exploit a vulnerability requiring physical access to a device, and therefore warrants a greater severity.
Attack Complexity: This metric captures measurable actions that must be taken by the attacker to actively evade or circumvent existing built-in security-enhancing conditions in order to obtain a working exploit. These are conditions whose primary purpose is to increase security and/or increase exploit engineering complexity. A vulnerability exploitable without a target-specific variable has a lower complexity than a vulnerability that would require non-trivial customization. This metric is meant to capture security mechanisms utilized by the vulnerable system.
Attack Requirements: This metric captures the prerequisite deployment and execution conditions or variables of the vulnerable system that enable the attack. These differ from security-enhancing techniques/technologies (ref Attack Complexity) as the primary purpose of these conditions is not to explicitly mitigate attacks, but rather, emerge naturally as a consequence of the deployment and execution of the vulnerable system.
Privileges Required: This metric describes the level of privileges an attacker must possess prior to successfully exploiting the vulnerability. The method by which the attacker obtains privileged credentials prior to the attack (e.g., free trial accounts), is outside the scope of this metric. Generally, self-service provisioned accounts do not constitute a privilege requirement if the attacker can grant themselves privileges as part of the attack.
User interaction: This metric captures the requirement for a human user, other than the attacker, to participate in the successful compromise of the vulnerable system. This metric determines whether the vulnerability can be exploited solely at the will of the attacker, or whether a separate user (or user-initiated process) must participate in some manner.
Vulnerable System Impact Metrics
Confidentiality: This metric measures the impact to the confidentiality of the information managed by the VULNERABLE SYSTEM due to a successfully exploited vulnerability. Confidentiality refers to limiting information access and disclosure to only authorized users, as well as preventing access by, or disclosure to, unauthorized ones.
Integrity: This metric measures the impact to integrity of a successfully exploited vulnerability. Integrity refers to the trustworthiness and veracity of information. Integrity of the VULNERABLE SYSTEM is impacted when an attacker makes unauthorized modification of system data. Integrity is also impacted when a system user can repudiate critical actions taken in the context of the system (e.g. due to insufficient logging).
Availability: This metric measures the impact to the availability of the VULNERABLE SYSTEM resulting from a successfully exploited vulnerability. While the Confidentiality and Integrity impact metrics apply to the loss of confidentiality or integrity of data (e.g., information, files) used by the system, this metric refers to the loss of availability of the impacted system itself, such as a networked service (e.g., web, database, email). Since availability refers to the accessibility of information resources, attacks that consume network bandwidth, processor cycles, or disk space all impact the availability of a system.
Subsequent System Impact Metrics
Confidentiality: This metric measures the impact to the confidentiality of the information managed by the SUBSEQUENT SYSTEM due to a successfully exploited vulnerability. Confidentiality refers to limiting information access and disclosure to only authorized users, as well as preventing access by, or disclosure to, unauthorized ones.
Integrity: This metric measures the impact to integrity of a successfully exploited vulnerability. Integrity refers to the trustworthiness and veracity of information. Integrity of the SUBSEQUENT SYSTEM is impacted when an attacker makes unauthorized modification of system data. Integrity is also impacted when a system user can repudiate critical actions taken in the context of the system (e.g. due to insufficient logging).
Availability: This metric measures the impact to the availability of the SUBSEQUENT SYSTEM resulting from a successfully exploited vulnerability. While the Confidentiality and Integrity impact metrics apply to the loss of confidentiality or integrity of data (e.g., information, files) used by the system, this metric refers to the loss of availability of the impacted system itself, such as a networked service (e.g., web, database, email). Since availability refers to the accessibility of information resources, attacks that consume network bandwidth, processor cycles, or disk space all impact the availability of a system.
CVSS:4.0/AV:N/AC:H/AT:N/PR:L/UI:N/VC:N/VI:H/VA:N/SC:N/SI:H/SA:N

CVE ID

CVE-2025-54584

Weaknesses

Misinterpretation of Input

The product misinterprets an input, whether from an attacker or another product, in a security-relevant fashion. Learn more on MITRE.

Credits