mandiant / mandiant/capa-rules
FP: decompress-using-aplib using IDA backend
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Description
The aplib rule currently misses on at least one variation of the aPLib code. https://github.com/secretsquirrel/the-backdoor-factory/blob/master/aPLib/src/64bit/depacks.asm . I cannot explain this failure, the first two checks hit with the comparison to 32000 and the compares against 127 and 128 match as well. Perhaps these constraints are invalid? https://github.com/fireeye/capa-rules/blob/a6d09ec94bfdd0d3e6561fa7eabfa8f79943bb95/data-manipulation/compression/decompress-data-using-aplib.yml#L29-L31
Sample hash is: aba89668c6e9681671a95b3d7a08aae2a067deed2d835ba6f6fd18556c88a5f2
Contributor guide
First steps
- Read the whole issue, then the project's contributing guide.
- Comment on the issue to say you are picking it up — it saves two people doing the same work.
- Fork the repository and make your change on a branch.
- Open a pull request that references the issue number.
Research direction
Start with data-manipulation/compression/decompress-data-using-aplib.yml, especially the constraints referenced near lines 29–31, and compare them with the 64-bit aPLib implementation in depacks.asm. Reproduce the miss using sample hash aba89668c6e9681671a95b3d7a08aae2a067deed2d835ba6f6fd18556c88a5f2 and determine which constraint fails; done means the rule recognizes this variation using the IDA backend.
Written by the indexing model from the issue text.
Assessment
- Domain
- reverse-engineering
- Issue type
- Bug
- Difficulty
- 4/5
- Estimated time
- 3-5 days
- Activity status
- Stale
- Clarity
- Needs clarification
- Newbie friendliness
- 35/100