Bug #4549: TCP reassembly, failed assert app_progress > last_ack_abs, both sides need to be pruned - Suricata - Open Information Security Foundation

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Bug #4549

closed

TCP reassembly, failed assert app_progress > last_ack_abs, both sides need to be pruned

Added by Philippe Antoine over 3 years ago. Updated over 2 years ago.

Status:

Closed

Priority:

Normal

Assignee:

Victor Julien

Target version:

7.0.0-beta1

Affected Versions:

6.0.3

Effort:

Difficulty:

Label:

Needs backport to 5.0, Needs backport to 6.0

Description

Found by oss-fuzz
https://bugs.chromium.org/p/oss-fuzz/issues/detail?id=35626

Minimized reproducer with suricata is
./src/suricata -r lolb.pcap -k none -c suricata.yaml --set stream.midstream=true

What happens is
- first packet (midstream) all ok (ack = 1)
- second packet, from the other side, ack is ok, but sequence indicates a gap from first packet ack (seq = 77)
- third packet, sequence ok, ack is increased since first packet confirming the gap (ack = 77) StreamTcpUpdateAppLayerProgress is called by AppLayerHandleTCPData at the end of if (flags & STREAM_GAP) {
- Fourth packet is in first direction (seq and ack meaningless)

At the end of third packet, the 76 gap does not get subtracted in app_progress_rel as StreamTcpPruneSession only considers the other stream

Files

lolb.pcap (984 Bytes) lolb.pcap

Philippe Antoine, 06/30/2021 07:26 PM

Related issues 2 (0 open — 2 closed)

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Updated by Philippe Antoine over 3 years ago

Side note : the fuzz target and suricata do not seem to handle the pcap timestamps the same way : Suricata does not crash on the original pcap because it did not time out a flow when the fuzz target did time it out (and so started a new one with the same flow hash)

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