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+---
+layout: blog.njk
+title: Making eBPF "Cursed Ping" Work on Linux, macOS, and BusyBox
+date: 2025-07-25
+description: How I made my eBPF ping hack universal
+---
+
+## Introduction
+
+Messing with ping using eBPF is fun-just mutate the timestamp in the ICMP Echo Reply and watch the round-trip time go wild!
+But in practice, different ping implementations use different payload formats. If you corrupt the wrong bytes, BSD/macOS ping will instantly complain about "wrong data byte".
+
+In this post, I’ll show how I made eBPF hack universal: it now works on Linux and macOS/BSD!
+
+---
+
+## The Problem
+
+- **Linux (iputils):** timestamp is 16 bytes (2 x uint64)
+- **macOS/BSD:** timestamp is only 8 bytes, followed by a signature sequence (0x08, 0x09, 0x0a, ...), which must not be touched!
+- **BusyBox:** timestamp is just 4 bytes (uint32_t)
+
+If you mutate the "extra" bytes, BSD ping immediately reports a corrupted payload.
+
+---
+
+## The Solution
+
+In the eBPF program, we:
+- Automatically detect the ping type by inspecting the payload signature
+- Mutate only the correct number of bytes:
+  - Linux: 16 bytes
+  - BSD/macOS: 8 bytes
+  - BusyBox: 4 bytes
+
+### Key eBPF Code Snippet
+
+```c
+__u8* payload = (void*)(icmphdr + 1);
+int ping_type = 0; // 0=linux, 1=bsd, 2=busybox
+
+if ((void*)(payload + 16) <= data_end) {
+    if (payload[8] == 0x08 && payload[9] == 0x09 && payload[10] == 0x0a && payload[11] == 0x0b) {
+        ping_type = 1; // BSD/macOS
+    }
+}
+if (ping_type == 0 && (void*)(payload + 8) <= data_end) {
+    if ((void*)(payload + 16) > data_end ||
+        (payload[8] != 0x08 && payload[9] != 0x09)) {
+        ping_type = 2; // BusyBox
+    }
+}
+
+if (ping_type == 2) {
+    __u32* ts_busybox = (void*)(icmphdr + 1);
+    if ((void*)(ts_busybox + 1) <= data_end) {
+        __u32 old_ts = *ts_busybox;
+        *ts_busybox -= bpf_get_prandom_u32() % 500;
+        recalc_icmp_csum(icmphdr, old_ts, *ts_busybox);
+    }
+} else if (ping_type == 1) {
+    __u64* ts_secs = (void*)(icmphdr + 1);
+    if ((void*)(ts_secs + 1) <= data_end) {
+        __u64 old_secs = *ts_secs;
+        *ts_secs -= bpf_get_prandom_u32() % 500;
+        recalc_icmp_csum(icmphdr, old_secs, *ts_secs);
+    }
+} else {
+    __u64* ts_secs = (void*)(icmphdr + 1);
+    if ((void*)(ts_secs + 1) <= data_end) {
+        __u64 old_secs = *ts_secs;
+        *ts_secs -= bpf_get_prandom_u32() % 500;
+        recalc_icmp_csum(icmphdr, old_secs, *ts_secs);
+    }
+    __u64* ts_nsecs = (void*)(icmphdr + 1) + sizeof(__u64);
+    if ((void*)ts_nsecs + sizeof(__u64) <= data_end) {
+        __u64 old_nsecs = *ts_nsecs;
+        *ts_nsecs -= bpf_get_prandom_u32();
+        recalc_icmp_csum(icmphdr, old_nsecs, *ts_nsecs);
+    }
+}
+```
+
+---
+
+## Real-World Examples
+
+### Linux (iputils):
+
+```bash
+$ ping 77.110.117.147
+PING 77.110.117.147 (77.110.117.147): 56 data bytes
+64 bytes from 77.110.117.147: icmp_seq=1 ttl=63 time=9796999 ms
+64 bytes from 77.110.117.147: icmp_seq=2 ttl=63 time=9997898 ms
+```
+
+### macOS/BSD:
+
+```bash
+platon@Moofbook~> ping 77.110.117.147
+PING 77.110.117.147 (77.110.117.147): 56 data bytes
+64 bytes from 77.110.117.147: icmp_seq=72 ttl=133 time=-872349695955.565 ms
+64 bytes from 77.110.117.147: icmp_seq=446 ttl=66 time=-368967679955.594 ms
+64 bytes from 77.110.117.147: icmp_seq=447 ttl=86 time=704643072044.353 ms
+^C
+--- 77.110.117.147 ping statistics ---
+3 packets transmitted, 3 packets received, 0.0% packet loss
+round-trip min/avg/max/stddev = -872349695955.565/-178891434622.269/704643072044.353/657684464294.250 ms
+```
+
+### BusyBox:
+
+```bash
+/ # ping 77.110.117.147
+PING 77.110.117.147 (77.110.117.147): 56 data bytes
+64 bytes from 77.110.117.147: seq=893 ttl=63 time=82.448 ms
+64 bytes from 77.110.117.147: seq=664 ttl=63 time=61.749 ms
+```
+> On busybox mutate ONLY seq (idk why)
+---
+
+## Conclusion
+
+Now our eBPF hack works on all major ping implementations, without breaking the payload or triggering "wrong data byte" errors.
+You can safely troll sysadmins and test network tools on any platform!
+
+---
+
+If you’re interested, the original source code is on [GitHub](https://github.com/x3lfyn/cursed-ping) and mine on [Github](https://github.com/crypetxctl/cursed-ping) and [own Gitea](https://git.iwakurahome.ru/lain/cursed-ping)