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GHSA-px8v-pp82-rcvr
No affected components available
Impact
An off-path attacker can inject an ICMP Packet Too Large packet. Since affected quic-go versions used IP_PMTUDISC_DO, the kernel would then return a "message too large" error on sendmsg, i.e. when quic-go attempts to send a packet that exceeds the MTU claimed in that ICMP packet.
By setting this value to smaller than 1200 bytes (the minimum MTU for QUIC), the attacker can disrupt a QUIC connection. Crucially, this can be done after completion of the handshake, thereby circumventing any TCP fallback that might be implemented on the application layer (for example, many browsers fall back to HTTP over TCP if they're unable to establish a QUIC connection).
As far as I understand, the kernel tracks the MTU per 4-tuple, so the attacker needs to at least know the client's IP and port tuple to mount an attack (assuming that it knows the server's IP and port).
Patches
The fix is easy: Use IP_PMTUDISC_PROBE instead of IP_PMTUDISC_DO. This socket option only sets the DF bit, but disables the kernel's MTU tracking.
Has the problem been patched? What versions should users upgrade to?
Fixed in https://github.com/quic-go/quic-go/pull/4729 Released in https://github.com/quic-go/quic-go/releases/tag/v0.48.2
Workarounds
Is there a way for users to fix or remediate the vulnerability without upgrading?
Use iptables to drop ICMP Unreachable packets.
References
Are there any links users can visit to find out more?
This bug was discovered while doing research for my new IETF draft on IP fragmentation: https://datatracker.ietf.org/doc/draft-seemann-tsvwg-udp-fragmentation/
The vulnerability can be exploited over a local network, such as Wi-Fi. It is easy for an attacker to exploit this vulnerability. An attacker does not need any special privileges or access rights. No user interaction is needed for the attacker to exploit this vulnerability. The impact is confined to the system where the vulnerability exists. There is a high impact on the availability of the system.
Exploitation attempts have been detected. Elevated vigilance and prompt remediation are advised.
The exploit probability is very low. The vulnerability is unlikely to be exploited in the next 30 days.
We did not find any exploit available. Neither in GitHub repositories nor in the Exploit-Database.
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