HL7 FHIR Partial Path Zip Slip due to bypass of CVE-2023-24057 (GHSA-9654-pr4f-gh6m)
Aliases: CVE-2023-28465
Published: 2023-03-10T22:15:55Z
Affected: [{'package': {'ecosystem': 'Maven', 'name': 'ca.uhn.hapi.fhir:org.hl7.fhir.core'}, 'ranges': [{'type': 'ECOSYSTEM', 'events': [{'introduced': '0'}, {'fixed': '5.6.106'}]}]}, {'package': {'ecosystem': 'Maven', 'name': 'ca.uhn.hapi.fhir:org.hl7.fhir.convertors'}, 'ranges': [{'type': 'ECOSYSTEM', 'events': [{'introduced': '0'}, {'fixed': '5.6.106'}]}]}, {'package': {'ecosystem': 'Maven', 'name': 'ca.uhn.hapi.fhir:org.hl7.fhir.r4b'}, 'ranges': [{'type': 'ECOSYSTEM', 'events': [{'introduced': '0'}, {'fixed': '5.6.106'}]}]}, {'package': {'ecosystem': 'Maven', 'name': 'ca.uhn.hapi.fhir:org.hl7.fhir.r5'}, 'ranges': [{'type': 'ECOSYSTEM', 'events': [{'introduced': '0'}, {'fixed': '5.6.106'}]}]}, {'package': {'ecosystem': 'Maven', 'name': 'ca.uhn.hapi.fhir:org.hl7.fhir.utilities'}, 'ranges': [{'type': 'ECOSYSTEM', 'events': [{'introduced': '0'}, {'fixed': '5.6.106'}]}]}, {'package': {'ecosystem': 'Maven', 'name': 'ca.uhn.hapi.fhir:org.hl7.fhir.validation'}, 'ranges': [{'type': 'ECOSYSTEM', 'events': [{'introduced': '0'}, {'fixed': '5.6.106'}]}]}]

### Impact

Zip Slip protections implemented in CVE-2023-24057 (GHSA-jqh6-9574-5x22) can be bypassed due a partial path traversal vulnerability.

This issue allows a malicious actor to potentially break out of the `TerminologyCacheManager` cache directory. The impact is limited to sibling directories.

To demonstrate the vulnerability, consider `userControlled.getCanonicalPath().startsWith("/usr/out")` will allow an attacker to access a directory with a name like `/usr/outnot`. 

### Why?

To demonstrate this vulnerability, consider `"/usr/outnot".startsWith("/usr/out")`.
The check is bypassed although `/outnot` is not under the `/out` directory.
It's important to understand that the terminating slash may be removed when using various `String` representations of the `File` object.
For example, on Linux, `println(new File("/var"))` will print `/var`, but `println(new File("/var", "/")` will print `/var/`;
however, `println(new File("/var", "/").getCanonicalPath())` will print `/var`.

### The Fix

Comparing paths with the `java.nio.files.Path#startsWith` will adequately protect againts this vulnerability.

For example: `file.getCanonicalFile().toPath().startsWith(BASE_DIRECTORY)` or `file.getCanonicalFile().toPath().startsWith(BASE_DIRECTORY_FILE.getCanonicalFile().toPath())`

### Other Examples

 - [CVE-2022-31159](https://github.com/aws/aws-sdk-java/security/advisories/GHSA-c28r-hw5m-5gv3) - aws/aws-sdk-java
 - [CVE-2022-23457](https://securitylab.github.com/advisories/GHSL-2022-008_The_OWASP_Enterprise_Security_API/) - ESAPI/esapi-java-legacy

### Vulnerability

https://github.com/hapifhir/org.hl7.fhir.core/blob/b0daf666725fa14476d147522155af1e81922aac/org.hl7.fhir.r4b/src/main/java/org/hl7/fhir/r4b/terminologies/TerminologyCacheManager.java#L99-L105

While `getAbsolutePath` will return a normalized path, because the string `path` is not slash terminated, the guard can be bypassed to write the contents of the Zip file to a sibling directory of the cache directory.

### Patches
All org.hl7.fhir.core libraries should be updated to 5.6.106.
 - https://github.com/hapifhir/org.hl7.fhir.core/pull/1162

### Workarounds
Unknown

### References
* https://snyk.io/research/zip-slip-vulnerability