vulnerabilities-workflow-1.md

Combined Vulnerability List for multierr Project

This document combines the identified vulnerabilities for the multierr project into a single list, removing any duplicates and formatting each vulnerability with detailed descriptions as requested.

• Vulnerability Name: Untrusted Error Implementation Leading to Panic in Error Formatting
  • Description: An attacker who can supply a custom error value with a malicious implementation of the Error() or Format() method can force a panic when the error is later formatted or logged through multierr. The steps to trigger this vulnerability are as follows:
    1. An attacker creates a custom error type (for example, a type named maliciousError) whose Error() method (or Format() method) deliberately panics.
    2. The attacker finds a way—for instance, through unvalidated input processing in the application—to have an instance of this malicious error injected into the error aggregation process (via calls to functions such as multierr.Combine() or multierr.Append()).
    3. When the application later formats the aggregated error (by calling its Error() method or using formatted output such as %+v), the multierr implementation calls the underlying error’s method without any protective wrapper.
    4. The malicious method panics, causing the overall error formatting operation to panic and, in turn, crash the application.
  • Impact: If this vulnerability is successfully triggered, it will cause an unexpected application crash due to an unhandled panic. In production, such a crash might lead to a loss of service and could also disrupt error logging and downstream monitoring—resulting in a potential denial of service situation.
  • Vulnerability Rank: High
  • Currently Implemented Mitigations:
    • The multierr library calls the Error() (and, if available, the Format() method) on each aggregated error without wrapping these calls in a recovery or sanitization mechanism.
    • There is no explicit input validation or error method sandboxing in the code (for example, in writeSingleline or writeMultiline).
  • Missing Mitigations:
    • A safe error-formatting wrapper that uses a recover() block to catch panics triggered by custom error methods should be introduced.
    • Optional validation or sanitization of error messages (especially when they could have originated from untrusted sources) would reduce the risk of a malicious error implementation.
  • Preconditions:
    • The application that uses multierr must allow error values (or errors derived from external inputs) that are controlled or influenced by an attacker.
    • The attacker must be able to inject a malicious error implementation into the error-handling path that is later aggregated by multierr.
  • Source Code Analysis:
    • In the function multiError.writeSingleline(w io.Writer) (found in error.go), the code iterates over the slice merr.errors and, for each item, immediately calls io.WriteString(w, item.Error()). There is no panic prevention mechanism (such as a deferred recover) around the call to item.Error().
    • Similarly, in multiError.writeMultiline(w io.Writer), the call to fmt.Sprintf("%+v", item) may invoke a custom Format() method on a user-controlled error value. Again, no recovery from panics is provided.
    • Because neither function attempts to catch panics resulting from calling methods on the aggregated error values, a malicious implementation that panics will propagate its panic and crash the caller.
  • Security Test Case:
    1. Setup:
       • Define a custom error type (e.g., maliciousError) whose Error() method immediately calls panic("malicious panic").
       • Create a benign error (for example, using errors.New("normal error")).
    2. Aggregation:
       • Use multierr.Combine(maliciousError{}, normalError) or a similar call (such as successive calls to multierr.Append()) to aggregate the malicious error with the benign error.
    3. Trigger:
       • Invoke the Error() method on the resulting aggregated error (or format it using fmt.Sprintf("%+v", aggregatedError)).
    4. Assertion:
       • Verify that the call panics as expected (this can be done by wrapping the call in a test that asserts a panic is raised).
    5. Result:
       • The successful detection of the panic confirms that an attacker who can inject such a malicious error would be able to cause a critical failure in any application that later formats the multierr error.