CVE-2022-49340 ip_gre: test csum_start instead of transport header
A missing validation in the Linux kernel GRE tunnel driver can cause an integer overflow, leading to a denial of service.
- Exploited in the wild
- Not known
- Login needed
- Any signed-in user
- Attackable
- Local or same network only
- Victim action needed
- Not needed
- Fix
- Available
What is CVE-2022-49340?
CVE-2022-49340 is a high-severity vulnerability in Linux kernel, published on 26 Feb 2025. It can only be exploited from the same machine or local network, with no action from the victim.
Official description
In the Linux kernel, the following vulnerability has been resolved:
ip_gre: test csum_start instead of transport header
GRE with TUNNEL_CSUM will apply local checksum offload on CHECKSUM_PARTIAL packets.
ipgre_xmit must validate csum_start after an optional skb_pull, else lco_csum may trigger an overflow. The original check was
if (csum && skb_checksum_start(skb) < skb->data) return -EINVAL;
This had false positives when skb_checksum_start is undefined: when ip_summed is not CHECKSUM_PARTIAL. A discussed refinement was straightforward
if (csum && skb->ip_summed == CHECKSUM_PARTIAL && skb_checksum_start(skb) < skb->data) return -EINVAL;
But was eventually revised more thoroughly: - restrict the check to the only branch where needed, in an uncommon GRE path that uses header_ops and calls skb_pull. - test skb_transport_header, which is set along with csum_start in skb_partial_csum_set in the normal header_ops datapath.
Turns out skbs can arrive in this branch without the transport header set, e.g., through BPF redirection.
Revise the check back to check csum_start directly, and only if CHECKSUM_PARTIAL. Do leave the check in the updated location. Check field regardless of whether TUNNEL_CSUM is configured.
Which versions are affected by CVE-2022-49340?
It affects 1 product.
Products include Linux kernel.
How do I fix CVE-2022-49340?
Apply the vendor's patch.
Is CVE-2022-49340 being exploited?
There is no known exploitation of CVE-2022-49340 in the wild and no public exploit code.
Other vulnerabilities in Linux kernel
Sources
Also known as DEBIAN-CVE-2022-49340, GHSA-4qqr-2jj8-h8q8, UBUNTU-CVE-2022-49340.