MITM based Zip Slip in `ca.uhn.hapi.fhir:org.hl7.fhir.core`

Impact

MITM can enable Zip-Slip.

Vulnerability

Vulnerability 1: Scanner.java

There is no validation that the zip file being unpacked has entries that are not maliciously writing outside of the intended destination directory.
https://github.com/hapifhir/org.hl7.fhir.core/blob/8c43e21094af971303131efd081503e5a112db4b/org.hl7.fhir.validation/src/main/java/org/hl7/fhir/validation/Scanner.java#L335-L357

This zip archive is downloaded over HTTP instead of HTTPS, leaving it vulnerable to compromise in-flight.
https://github.com/hapifhir/org.hl7.fhir.core/blob/8c43e21094af971303131efd081503e5a112db4b/org.hl7.fhir.validation/src/main/java/org/hl7/fhir/validation/Scanner.java#L136

Vulnerability 2: TerminologyCacheManager.java

Note: While these links point to only one implementation, both implementations of TerminologyCacheManager.java are vulnerable to this as their code seems to be duplicated.

• https://github.com/hapifhir/org.hl7.fhir.core/blob/f58b7acfb5e393cac52cc5bbb170bdb669c2880e/org.hl7.fhir.r5/src/main/java/org/hl7/fhir/r5/terminologies/TerminologyCacheManager.java
• https://github.com/hapifhir/org.hl7.fhir.core/blob/f58b7acfb5e393cac52cc5bbb170bdb669c2880e/org.hl7.fhir.r4b/src/main/java/org/hl7/fhir/r4b/terminologies/TerminologyCacheManager.java

While there is validation in this bit of logic that attempts to validate that the zip file doesn’t contain malicious entries that escape the destination directory, the guard is insufficient.

https://github.com/hapifhir/org.hl7.fhir.core/blob/f58b7acfb5e393cac52cc5bbb170bdb669c2880e/org.hl7.fhir.r5/src/main/java/org/hl7/fhir/r5/terminologies/TerminologyCacheManager.java#L97-L113

This is because the Utilities.path(String... path) method does not normalize the path, although it seems to be attempting to do so.
https://github.com/hapifhir/org.hl7.fhir.core/blob/f58b7acfb5e393cac52cc5bbb170bdb669c2880e/org.hl7.fhir.utilities/src/main/java/org/hl7/fhir/utilities/Utilities.java#L617-L675

The normalization only occurs if the path element starts with a path traversal payload. As an example, calling Utilities.path("/base", "/child/../test") will return the string "/base/child/../test".

This guard logic can, thus, be easily bypassed:
https://github.com/hapifhir/org.hl7.fhir.core/blob/f58b7acfb5e393cac52cc5bbb170bdb669c2880e/org.hl7.fhir.r5/src/main/java/org/hl7/fhir/r5/terminologies/TerminologyCacheManager.java#L100-L104

Assuming an attacker can control the return value of ze.getName(), they can supply a value like /anything/../../../../zipsip-protection-bypass.txt.

Similarly, an attacker can control the contents of the Zip file via a MITM attack as this logic is used with resources not downloaded over HTTPS.

https://github.com/hapifhir/org.hl7.fhir.core/blob/f58b7acfb5e393cac52cc5bbb170bdb669c2880e/org.hl7.fhir.r5/src/main/java/org/hl7/fhir/r5/terminologies/TerminologyCacheManager.java#L66-L73

Patches

Unknown

Workarounds

Unknown

References

• https://snyk.io/research/zip-slip-vulnerability