{
  "affected": [
    {
      "ecosystem_specific": {
        "urgency": "not yet assigned"
      },
      "package": {
        "ecosystem": "Debian:12",
        "name": "linux"
      },
      "ranges": [
        {
          "events": [
            {
              "introduced": "0"
            }
          ],
          "type": "ECOSYSTEM"
        }
      ]
    },
    {
      "ecosystem_specific": {
        "urgency": "not yet assigned"
      },
      "package": {
        "ecosystem": "Debian:13",
        "name": "linux"
      },
      "ranges": [
        {
          "events": [
            {
              "introduced": "0"
            }
          ],
          "type": "ECOSYSTEM"
        }
      ]
    },
    {
      "ecosystem_specific": {
        "urgency": "not yet assigned"
      },
      "package": {
        "ecosystem": "Debian:14",
        "name": "linux"
      },
      "ranges": [
        {
          "events": [
            {
              "introduced": "0"
            }
          ],
          "type": "ECOSYSTEM"
        }
      ]
    }
  ],
  "details": "In the Linux kernel, the following vulnerability has been resolved:  ppp_async: drop the errored frame instead of resetting its headroom  ppp_receive_nonmp_frame() prepends a two-byte direction tag before running the pass/active BPF filters:  \t*(__be16 *)skb_push(skb, 2) = htons(PPP_FILTER_INBOUND_TAG);  Nothing on the receive path guarantees those two bytes of headroom. The frame-error path in ppp_async's process_input_packet() resets a reused skb's headroom to zero while claiming to restore it to a freshly allocated state - but a fresh skb from dev_alloc_skb() carries NET_SKB_PAD:  \terr: \t\tif (skb) { \t\t\t/* make skb appear as freshly allocated */ \t\t\tskb_trim(skb, 0); \t\t\tskb_reserve(skb, - skb_headroom(skb)); \t\t}  ap-\u003erpkt still points at that skb, so the next frame is reassembled into it with no headroom at all. A peer that sends a bad-FCS frame followed by one beginning ff 03 then leaves a single byte of headroom by the time the filter tag is pushed, which lands one byte below skb-\u003ehead:    skbuff: skb_under_panic: len:49 put:2 head:ffff888003c10000           data:ffff888003c0ffff tail:0x30 end:0x640 dev:\u003cNULL\u003e   kernel BUG at net/core/skbuff.c:214!   RIP: 0010:skb_panic+0x13e/0x230   Call Trace:    skb_push+0xbd/0x100    ppp_receive_nonmp_frame+0x48a/0x1d10    ppp_input+0x4e9/0x2f80    ppp_async_process+0x2a/0xe0    tasklet_action_common+0x20f/0x8a0    handle_softirqs+0x18e/0x590   Kernel panic - not syncing: Fatal exception in interrupt  Zeroing the headroom violates the NET_SKB_PAD guarantee that dev_alloc_skb() gives the rest of the receive path. Besides the filter panic above, when CCP compression is enabled ppp_decompress_frame() hands skb-\u003edata - 2 to -\u003edecompress()/-\u003eincomp(), which then reads out of bounds before skb-\u003ehead for the same reason.  Rather than restore the headroom, drop the errored frame - as ppp_synctty already does on its error path - and clear ap-\u003erpkt so the next frame is reassembled into a fresh skb with proper headroom. This is simpler and fixes both the filter under-panic and the CCP out-of-bounds read.  The original V1 of this patch made room in ppp_receive_nonmp_frame() with skb_cow_head(); Eric pointed out that fixing the root cause in the transport is the right approach.  Found by fuzzing the PPP receive path with a mutating peer on a pty; it is an interesting (remote) DoS: root configures PPP, the peer supplies two crashing frames. The reproducer (repro-ppp-skb.c, unchanged from v1) panics in about a second, and returns cleanly with this applied.",
  "id": "DEBIAN-CVE-2026-98158",
  "modified": "2026-09-26T04:47:28.396139593Z",
  "published": "2026-09-25T11:17:47.510Z",
  "references": [
    {
      "type": "ADVISORY",
      "url": "https://security-tracker.debian.org/tracker/CVE-2026-98158"
    }
  ],
  "upstream": [
    "CVE-2026-98158"
  ]
}