The UNIX editor Vim prior to version 9.1.0678 has a use-after-free error in argument list handling. When adding a new file to the argument list, this triggers Buf* autocommands. If in such an autocommand the buffer that was just opened is closed (including the window where it is shown), this causes the window structure to be freed which contains a reference to the argument list that we are actually modifying. Once the autocommands are completed, the references to the window and argument list are no longer valid and as such cause an use-after-free. Impact is low since the user must either intentionally add some unusual autocommands that wipe a buffer during creation (either manually or by sourcing a malicious plugin), but it will crash Vim. The issue has been fixed as of Vim patch v9.1.0678.
Referencing memory after it has been freed can cause a program to crash, use unexpected values, or execute code.
| Name | Vendor | Start Version | End Version |
|---|---|---|---|
| Vim | Ubuntu | devel | * |
| Vim | Ubuntu | esm-infra/bionic | * |
| Vim | Ubuntu | esm-infra/xenial | * |
| Vim | Ubuntu | focal | * |
| Vim | Ubuntu | jammy | * |
| Vim | Ubuntu | noble | * |
| Vim | Ubuntu | trusty/esm | * |
| Vim | Ubuntu | upstream | * |
The use of previously-freed memory can have any number of adverse consequences, ranging from the corruption of valid data to the execution of arbitrary code, depending on the instantiation and timing of the flaw. The simplest way data corruption may occur involves the system’s reuse of the freed memory. Use-after-free errors have two common and sometimes overlapping causes:
In this scenario, the memory in question is allocated to another pointer validly at some point after it has been freed. The original pointer to the freed memory is used again and points to somewhere within the new allocation. As the data is changed, it corrupts the validly used memory; this induces undefined behavior in the process. If the newly allocated data happens to hold a class, in C++ for example, various function pointers may be scattered within the heap data. If one of these function pointers is overwritten with an address to valid shellcode, execution of arbitrary code can be achieved.