Summary
A high-severity integer underflow and response-length validation flaw in libIEC61850's MMS file service can cause file-read responses to include stale data from a reused connection buffer.
When the file service is enabled, an unauthenticated remote client may be able to disclose prior response data, protocol fragments, or other residual memory contents by supplying an out-of-range file position.
A high-severity integer underflow and response-length validation flaw in libIEC61850's MMS file service can cause file-read responses to include stale data from a reused connection buffer.
When the file service is enabled, an unauthenticated remote client may be able to disclose prior response data, protocol fragments, or other residual memory contents by supplying an out-of-range file position.
Affected context
The issue occurs in libIEC61850 versions before 1.6.2 when the MMS file service is enabled and processes file-open and file-read requests over a remote connection.
Risk is higher when connection buffers are reused, file positions are not constrained to the requested file size, and response construction does not enforce the number of bytes actually returned by the filesystem.
The issue occurs in libIEC61850 versions before 1.6.2 when the MMS file service is enabled and processes file-open and file-read requests over a remote connection.
Risk is higher when connection buffers are reused, file positions are not constrained to the requested file size, and response construction does not enforce the number of bytes actually returned by the filesystem.
Exploit preconditions
- Attack surface: Network-accessible MMS file service
- Required access: Remote client access to the enabled service; authentication is not necessarily required
- Trigger point: Processing of file-open and subsequent file-read operations
- Why exploitation is possible: An out-of-range initial position can cause unsigned arithmetic to produce an excessive remaining-length calculation, while the response path may transmit more data than the filesystem actually read
- Attack surface: Network-accessible MMS file service
- Required access: Remote client access to the enabled service; authentication is not necessarily required
- Trigger point: Processing of file-open and subsequent file-read operations
- Why exploitation is possible: An out-of-range initial position can cause unsigned arithmetic to produce an excessive remaining-length calculation, while the response path may transmit more data than the filesystem actually read
Why this happens
The vulnerability results from accepting a file position outside the valid file range and retaining it in the file-read state without adequate bounds enforcement.
Subsequent unsigned subtraction between the file size and the larger read position can wrap to a very large value. Because response construction is not sufficiently limited by the actual filesystem-read result, stale bytes remaining in a reused connection buffer may be exposed. This maps primarily to CWE-191: Integer Underflow or Wraparound, with related consequences described by CWE-200: Exposure of Sensitive Information and CWE-252: Unchecked Return Value.
The vulnerability results from accepting a file position outside the valid file range and retaining it in the file-read state without adequate bounds enforcement.
Subsequent unsigned subtraction between the file size and the larger read position can wrap to a very large value. Because response construction is not sufficiently limited by the actual filesystem-read result, stale bytes remaining in a reused connection buffer may be exposed. This maps primarily to CWE-191: Integer Underflow or Wraparound, with related consequences described by CWE-200: Exposure of Sensitive Information and CWE-252: Unchecked Return Value.
Potential impact
- An attacker may disclose stale response data from a reused connection buffer
- Protocol fragments or information from earlier requests could be exposed
- Sensitive application or operational data may be revealed
- Repeated requests could increase the amount of residual data disclosed
- The service could experience malformed or resource-intensive response handling
- An attacker may disclose stale response data from a reused connection buffer
- Protocol fragments or information from earlier requests could be exposed
- Sensitive application or operational data may be revealed
- Repeated requests could increase the amount of residual data disclosed
- The service could experience malformed or resource-intensive response handling
General mitigation guidance
Mitigation typically focuses on enforcing numeric bounds and ensuring that response lengths reflect trusted, successfully read data.
Common defensive patterns include:
- Rejecting file positions that are negative, out of range, or inconsistent with the file size before storing read state
- Using overflow-aware arithmetic and validating subtraction operands before calculation
- Limiting every response to the actual number of bytes returned by the filesystem layer
- Clearing or tightly bounding reusable connection buffers before transmission
- Treating filesystem return values and byte counts as mandatory validation inputs
- Disabling the MMS file service when it is not required
- Applying authentication, network segmentation, and least-privilege service permissions
Mitigation typically focuses on enforcing numeric bounds and ensuring that response lengths reflect trusted, successfully read data.
Common defensive patterns include:
- Rejecting file positions that are negative, out of range, or inconsistent with the file size before storing read state
- Using overflow-aware arithmetic and validating subtraction operands before calculation
- Limiting every response to the actual number of bytes returned by the filesystem layer
- Clearing or tightly bounding reusable connection buffers before transmission
- Treating filesystem return values and byte counts as mandatory validation inputs
- Disabling the MMS file service when it is not required
- Applying authentication, network segmentation, and least-privilege service permissions
How teams detect issues like this
Organizations can detect this class of issue through:
- Static analysis for unsigned subtraction involving externally controlled offsets and file sizes
- Checks for response lengths derived from requested ranges rather than actual read results
- Code review of file-service state transitions and reusable network-buffer handling
- Fuzzing with boundary, oversized, and out-of-range file positions
- Runtime monitoring for unusually large responses or repeated file-read requests
- Policy enforcement requiring bounds checks and return-value validation in protocol handlers
Automated code review and security-analysis tools may help identify arithmetic-wraparound and unchecked-result patterns early.
Organizations can detect this class of issue through:
- Static analysis for unsigned subtraction involving externally controlled offsets and file sizes
- Checks for response lengths derived from requested ranges rather than actual read results
- Code review of file-service state transitions and reusable network-buffer handling
- Fuzzing with boundary, oversized, and out-of-range file positions
- Runtime monitoring for unusually large responses or repeated file-read requests
- Policy enforcement requiring bounds checks and return-value validation in protocol handlers
Automated code review and security-analysis tools may help identify arithmetic-wraparound and unchecked-result patterns early.
