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Combined Vulnerability List for slog-shim Project

The following vulnerabilities were identified in the slog-shim project.

1. Log Forging via Unsanitized Input in Text Logging Handler

Description: An external attacker who can supply data that eventually gets logged may craft messages containing newline characters or additional key=value pairs. When an application using this shim logs such unsanitized user input (for example, via the TextHandler), the output can be split into multiple log “lines” that appear to be separate log entries. An attacker could use this behavior to forge log entries or obscure their own activities in audit trails.

Impact: Forged or mangled log entries may mislead operators or automated log analysis systems. This undermines the integrity of audit trails and can make forensic analysis more difficult during an incident response—potentially aiding an attacker in covering their tracks or injecting misleading security events.

Vulnerability Rank: High

Currently Implemented Mitigations:

  • The project simply delegates log formatting to the underlying implementations (either Go’s official log/slog in Go 1.21 or golang.org/x/exp/slog in earlier versions).
  • There is no extra sanitization added in the slog‑shim code to escape or filter newline characters or log delimiters.

Missing Mitigations:

  • Input sanitization and output encoding need to be applied to any untrusted string values before they are handed off to the logging handler.
  • The TextHandler (and any handler that produces plain‑text output) should escape, filter, or otherwise neutralize control characters (e.g. newline characters) that could be abused for log forging.

Preconditions:

  • The deployed system uses slog‑shim and configures a plain‑text logging handler (via NewTextHandler) to write log files or send log messages to a log collector.
  • User‑supplied input (or any untrusted string data) is logged without additional sanitization.

Source Code Analysis:

  • In both text_handler.go (for Go 1.21) and text_handler_120.go (for earlier Go versions), the shim simply wraps the underlying slog.NewTextHandler without adding any sanitization.
  • The underlying handler joins key=value pairs with space delimiters and appends a newline at the end. If any logged message or attribute contains embedded newline characters (or characters that mimic key/value separators), the output is not corrected or escaped.

Security Test Case:

  1. Deploy an instance of an application that uses slog‑shim with the TextHandler configured to write to a log file.
  2. Locate an endpoint or input field which eventually is logged by the system.
  3. Send a request in which one of the parameters includes a payload such as: 
    normal_message\nFakeKey=FakeValue
  4. Examine the log file to verify that the log entry has been split into two lines and that a forged entry (e.g. “FakeKey=FakeValue”) appears as a separate log field.
  5. Confirm that the unsanitized newlines in the log output can be used to mislead log parsers or auditors.

2. Use of an Archived Logging Shim (Unmaintained Code)

Description: The project README clearly indicates that the shim is archived and recommends direct usage of the standard log/slog package instead. As an archived project, the slog‑shim will no longer receive active maintenance or security patches. An attacker reviewing the source code and underlying dependencies (including the experimental golang.org/x/exp/slog used as a fallback on pre‑Go 1.21 systems) may identify vulnerabilities that will remain unpatched in this shim.

Impact: Systems that continue to use slog‑shim instead of migrating to an actively maintained logging library risk exposure to new or unpatched vulnerabilities in the shim itself or in its underlying dependencies. In a production environment, this maintenance risk can lead to a long‑term security gap that attackers may exploit.

Vulnerability Rank: Critical

Currently Implemented Mitigations:

  • The README warns potential users that the project is archived and advises using the official slog package directly on Go 1.21 and later.

Missing Mitigations:

  • The project is not actively maintained, and no additional patches or security hardening measures are in place to address future vulnerabilities that may be discovered.
  • There is no migration path enforced in the code—systems may continue to depend on an unmaintained shim.

Preconditions:

  • The deployed system uses slog‑shim from this repository in production—especially on systems that remain on Go versions that trigger the fallback code using golang.org/x/exp/slog.
  • An attacker identifies or exploits a vulnerability in either the shim or its underlying logging implementations.

Source Code Analysis:

  • The entire library is essentially a pass‑through exposing either the experimental golang.org/x/exp/slog (for Go versions below 1.21) or the official log/slog for newer versions.
  • The archived status noted in the README means that no further security improvements or bug fixes will be made, leaving any discovered issues unremediated.

Security Test Case:

  1. Review the project’s README and commit history to confirm its archived status.
  2. Identify a known vulnerability (or simulate one) in the underlying dependency (e.g. a security advisory found later for golang.org/x/exp/slog).
  3. Deploy a system that uses slog‑shim built for Go versions below 1.21 (thus using the vulnerable fallback).
  4. Demonstrate that the vulnerability is exploitable due to the absence of back‑ported security fixes in the archived shim code.
  5. Validate that a system using slog‑shim remains exposed even after the vulnerability is publicly documented.