{"id":"DEBIAN-CVE-2026-68124","details":"In the Linux kernel, the following vulnerability has been resolved:  mctp: serial: handle zero-length frames to prevent rx buffer overflow  The MCTP serial receive state machine reads a frame length byte in mctp_serial_push_header() case 2 and validates it upper-bound-only:  \tif (c \u003e MCTP_SERIAL_FRAME_MTU) { \t\tdev-\u003erxstate = STATE_ERR; \t} else { \t\tdev-\u003erxlen = c; \t\tdev-\u003erxpos = 0; \t\tdev-\u003erxstate = STATE_DATA; \t\t... \t}  A length of zero passes this check, so rxlen is set to 0 and the state machine advances to STATE_DATA. In mctp_serial_push() STATE_DATA, the incoming byte is stored and rxpos incremented before the terminator is  \tdev-\u003erxbuf[dev-\u003erxpos] = c; \tdev-\u003erxpos++; \tdev-\u003erxstate = STATE_DATA; \tif (dev-\u003erxpos == dev-\u003erxlen) { \t\tdev-\u003erxpos = 0; \t\tdev-\u003erxstate = STATE_TRAILER; \t}  With rxlen == 0 the \"rxpos == rxlen\" terminator can never fire (rxpos is already 1 on the first data byte), so subsequent bytes are written past the end of the fixed 74-byte rxbuf, which is the last member of the netdev private area. Every following data byte is an attacker-controlled 1-byte out-of-bounds heap write, and the overflow continues until a frame (0x7e) or escape byte resets the parser -- effectively unbounded.  Reaching this requires CAP_NET_ADMIN to attach the N_MCTP line discipline and bring the resulting mctpserialN netdev up, after which the bytes arrive via the tty receive path.  Route a zero-length frame straight to STATE_TRAILER instead of STATE_DATA. The trailer/framing bytes are still consumed, and the frame resolves to a zero-length skb that the MCTP core rejects; the parser never enters STATE_DATA with rxlen == 0, so the out-of-bounds write can no longer occur.  KASAN, on a frame of 0x7e 0x01 0x00 followed by data bytes (before this change):    UBSAN: array-index-out-of-bounds in drivers/net/mctp/mctp-serial.c:370   index 74 is out of range for type 'u8 [74]'   BUG: KASAN: slab-out-of-bounds in mctp_serial_tty_receive_buf   Write of size 1 at addr ... by task kworker/u16:0    mctp_serial_tty_receive_buf    tty_ldisc_receive_buf    flush_to_ldisc   Allocated by task 152:    alloc_netdev_mqs    mctp_serial_open  v2: route zero-length frames to STATE_TRAILER instead of STATE_ERR so     the trailer/framing bytes are still consumed (Jeremy Kerr).  Found by 0sec automated security-research tooling (https://0sec.ai).","modified":"2026-09-08T17:00:16.587964794Z","published":"2026-08-10T13:19:57.550Z","upstream":["CVE-2026-68124"],"references":[{"type":"ADVISORY","url":"https://security-tracker.debian.org/tracker/CVE-2026-68124"}],"affected":[{"package":{"name":"linux","ecosystem":"Debian:12","purl":"pkg:deb/debian/linux?arch=source&distro=bookworm"},"ranges":[{"type":"ECOSYSTEM","events":[{"introduced":"0"},{"fixed":"6.1.187-1"}]}],"versions":["6.1.106-1","6.1.106-2","6.1.106-3","6.1.112-1","6.1.115-1","6.1.119-1","6.1.123-1","6.1.124-1","6.1.128-1","6.1.129-1","6.1.133-1","6.1.135-1","6.1.137-1","6.1.139-1","6.1.140-1","6.1.147-1","6.1.148-1","6.1.153-1","6.1.158-1","6.1.159-1","6.1.162-1","6.1.164-1","6.1.170-1","6.1.170-2","6.1.170-3","6.1.172-1","6.1.174-1","6.1.176-1","6.1.177-1","6.1.180-1","6.1.27-1","6.1.37-1","6.1.38-1","6.1.38-2","6.1.38-2~bpo11+1","6.1.38-3","6.1.38-4","6.1.38-4~bpo11+1","6.1.52-1","6.1.55-1","6.1.55-1~bpo11+1","6.1.64-1","6.1.66-1","6.1.67-1","6.1.69-1","6.1.69-1~bpo11+1","6.1.76-1","6.1.76-1~bpo11+1","6.1.82-1","6.1.85-1","6.1.90-1","6.1.90-1~bpo11+1","6.1.94-1","6.1.94-1~bpo11+1","6.1.98-1","6.1.99-1"],"ecosystem_specific":{"urgency":"not 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