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GHSA-6845-xw22-ffxv
No affected components available
Summary
There is an error in the stack management when compiling the IR for sha3_64. Concretely, the height variable is miscalculated.
The vulnerability can't be triggered without writing the IR by hand. That is, it cannot be triggered from regular vyper code, it can only be triggered by using the fang binary directly (this binary used to be called vyper-ir prior to v0.3.4).
Details
To compile sha3_64, the arg[0] and arg[1] have to be compiled:
https://github.com/vyperlang/vyper/blob/c150fc49ee9375a930d177044559b83cb95f7963/vyper/ir/compile_ir.py#L585-L586
As can be seen, after compiling the 0th arg, the height variable isn't increased. If new withargs are defined in the inner scope, they are manipulated correctly, because both their height is off and also the global height is off and thus their placement on the stack is computed correctly.
sha3_64 is used for retrieval in mappings. No flow that would cache the key was found, the issue shouldn't be possible to trigger when compiling the compiler-generated IR.
PoC
Suppose the following hand-written IR:
(with _loc
(with val 1
(with key 2
(sha3_64 val key)))
(seq
(sstore _loc
(with x (sload _loc)
(with ans (add x 1) (seq (assert (ge ans x)) ans))))))
after compilation:
the generated bytecode: 6001600281806020525f5260405f2090509050805460018101818110610026579050815550005b5f80fd
0000 60 PUSH1 0x01
0002 60 PUSH1 0x02
0004 81 DUP2
0005 80 DUP1 *********** bad code here!!!!!!
0006 60 PUSH1 0x20
0008 52 MSTORE
It can be seen that the second DUP will dup the item on the top of the stack which is incorrect.
Patches
Patched in https://github.com/vyperlang/vyper/pull/4063.
Impact
Versions v0.2.0-v0.3.10 were evaluated, and access of the variable with the invalid height is not reachable from IR generated by the vyper front-end. Because the issue isn't triggered during normal compilation of vyper code, the impact is considered low.
The vulnerability can be exploited over the network without needing physical access. It is difficult for an attacker to exploit this vulnerability and may require special conditions. An attacker does not need any special privileges or access rights. No user interaction is needed for the attacker to exploit this vulnerability. The impact is confined to the system where the vulnerability exists. There is a low impact on the confidentiality of the information.
Limited exploitation activity has been observed. Close monitoring and planned remediation are recommended.
The exploit probability is very low. The vulnerability is unlikely to be exploited in the next 30 days.
We did not find any exploit available. Neither in GitHub repositories nor in the Exploit-Database.
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