Unbounded TLV length in ReadFile can cause Denial of Service
Summary
A Denial of Service vulnerability was identified in ReadFile() where unbounded TLV length values could lead to excessive CPU and memory usage when processing data from a malicious or non-compliant NFC source. This issue has been fixed by enforcing strict limits on acceptable TLV lengths.
Affected Versions
- Affected: All versions prior to v0.17.2
- Fixed in: v0.17.2
Details
ReadFile() processes BER-TLV encoded data returned from an NFC or APDU source via a Transceiver interface. Prior to the fix, the implementation did not enforce an upper bound on long-form TLV length values.
A malicious or non-compliant NFC endpoint could advertise an excessively large length (up to 4 GB), causing the library to:
- Perform a very large number of read iterations
- Allocate excessive memory
- Consume significant CPU resources
- Block execution for an extended period
While such lengths are unrealistic for compliant MRTD or ISO 7816 devices, they can be produced by emulated or malicious sources, or by untrusted inputs routed through higher-level APIs.
Impact
Applications using gmrtd to read data from NFC or APDU sources may experience:
- Excessive CPU usage
- Memory exhaustion
- Application hangs or denial of service
No confidentiality or data integrity impact has been identified.
Resolution
This issue has been resolved in v0.17.2.
The fix introduces:
- Enforcement of maximum allowable TLV lengths
- Upper bounds on the number of read operations required to retrieve a file
- Rejection of APDUs that exceed the requested response length
Recommendation
Users should upgrade to v0.17.2 or later.
No additional mitigation is required once the library is updated.
Credits
Discovered and reported by @ramrunner.
NVD description
gmrtd is a Go library for reading Machine Readable Travel Documents (MRTDs). Prior to version 0.17.2, ReadFile accepts TLVs with lengths that can range up to 4GB, which can cause unconstrained resource consumption in both memory and cpu cycles. ReadFile can consume an extended TLV with lengths well outside what would be available in ICs. It can accept something all the way up to 4GB which would take too many iterations in 256 byte chunks, and would also try to allocate memory that might not be available in constrained environments like phones. Or if an API sends data to ReadFile, the same problem applies. The very small chunked read also locks the goroutine in accepting data for a very large number of iterations. projects using the gmrtd library to read files from NFCs can experience extreme slowdowns or memory consumption. A malicious NFC can just behave like the mock transceiver described above and by just sending dummy bytes as each chunk to be read, can make the receiving thread unresponsive and fill up memory on the host system. Version 0.17.2 patches the issue.