{"id":"CVE-2026-45842","url":"https://www.cyber-defence.io/tools/cve/CVE-2026-45842","generatedAt":"2026-10-28T03:41:20.366Z","title":"In the Linux kernel, the following vulnerability has been resolved: slip: reject VJ receive packets on instances with no rstate array slhc_init() accepts rslots == 0 as a valid configuration, with the documented meaning of 'no receive compression'.","description":"In the Linux kernel, the following vulnerability has been resolved:\n\nslip: reject VJ receive packets on instances with no rstate array\n\nslhc_init() accepts rslots == 0 as a valid configuration, with the\ndocumented meaning of 'no receive compression'. In that case the\nallocation loop in slhc_init() is skipped, so comp->rstate stays\nNULL and comp->rslot_limit stays 0 (from the kzalloc of struct\nslcompress).\n\nThe receive helpers do not defend against that configuration.\nslhc_uncompress() dereferences comp->rstate[x] when the VJ header\ncarries an explicit connection ID, and slhc_remember() later assigns\ncs = &comp->rstate[...] after only comparing the packet's slot number\nto comp->rslot_limit. Because rslot_limit is 0, slot 0 passes the\nrange check, and the code dereferences a NULL rstate.\n\nThe configuration is reachable in-tree through PPP. PPPIOCSMAXCID\nstores its argument in a signed int, and (val >> 16) uses arithmetic\nshift. Passing 0xffff0000 therefore sign-extends to -1, so val2 + 1\nis 0 and ppp_generic.c ends up calling slhc_init(0, 1). Because\n/dev/ppp open is gated by ns_capable(CAP_NET_ADMIN), the whole path\nis reachable from an unprivileged user namespace. Once the malformed\nVJ state is installed, any inbound VJ-compressed or VJ-uncompressed\nframe that selects slot 0 crashes the kernel in softirq context:\n\n Oops: general protection fault, probably for non-canonical\n       address 0xdffffc0000000000: 0000 [#1] SMP KASAN NOPTI\n KASAN: null-ptr-deref in range [0x0000000000000000-0x0000000000000007]\n RIP: 0010:slhc_uncompress (drivers/net/slip/slhc.c:519)\n Call Trace:\n  <TASK>\n  ppp_receive_nonmp_frame (drivers/net/ppp/ppp_generic.c:2466)\n  ppp_input (drivers/net/ppp/ppp_generic.c:2359)\n  ppp_async_process (drivers/net/ppp/ppp_async.c:492)\n  tasklet_action_common (kernel/softirq.c:926)\n  handle_softirqs (kernel/softirq.c:623)\n  run_ksoftirqd (kernel/softirq.c:1055)\n  smpboot_thread_fn (kernel/smpboot.c:160)\n  kthread (kernel/kthread.c:436)\n  ret_from_fork (arch/x86/kernel/process.c:164)\n  </TASK>\n\nReject the receive side on such instances instead of touching rstate.\nslhc_uncompress() falls through to its existing 'bad' label, which\nbumps sls_i_error and enters the toss state. slhc_remember() mirrors\nthat with an explicit sls_i_error increment followed by slhc_toss();\nthe sls_i_runt counter is not used here because a missing rstate is\nan internal configuration state, not a runt packet.\n\nThe transmit path is unaffected: the only in-tree caller that picks\nrslots from userspace (ppp_generic.c) still supplies tslots >= 1, and\nslip.c always calls slhc_init(16, 16), so comp->tstate remains valid\nand slhc_compress() continues to work.","published":"2026-05-27T11:16:24.000Z","lastModified":"2026-10-15T02:19:37.000Z","status":"Modified","sourceIdentifier":"416baaa9-dc9f-4396-8d5f-8c081fb06d67","cvss":{"version":"3.1","score":5.5,"severity":"MEDIUM","vector":"CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H"},"cwe":["CWE-476"],"affected":["linux/linux kernel"],"epss":{"score":0.00129,"percentile":0.02569,"date":"2026-10-27","history":[]},"kev":{"listed":false},"exploits":{"count":0,"verified":false,"firstPublished":null,"source":"Exploit-DB (https://gitlab.com/exploit-database/exploitdb)","entries":[]},"verdict":{"level":"low","text":"Lower severity and a low EPSS score (0.13%). Track it; it rarely justifies an emergency change on its own."},"changes":[],"references":[{"url":"https://git.kernel.org/stable/c/3d71c961febddd855d3ae9a519eeb96c8023f430","tags":["Patch"],"source":"416baaa9-dc9f-4396-8d5f-8c081fb06d67"},{"url":"https://git.kernel.org/stable/c/4aa9eca6fda2919027dfd7a7cc69334982d89586","tags":["Patch"],"source":"416baaa9-dc9f-4396-8d5f-8c081fb06d67"},{"url":"https://git.kernel.org/stable/c/72304fec672e8aac9ee7b9c475db96b37cca8d8d","tags":["Patch"],"source":"416baaa9-dc9f-4396-8d5f-8c081fb06d67"},{"url":"https://git.kernel.org/stable/c/7b0d9e878ec2b21d99ae8051b3dda59cdb66c152","tags":["Patch"],"source":"416baaa9-dc9f-4396-8d5f-8c081fb06d67"},{"url":"https://git.kernel.org/stable/c/9e1ff0eead073c4f46d874ad2526b7dda5465faf","tags":["Patch"],"source":"416baaa9-dc9f-4396-8d5f-8c081fb06d67"},{"url":"https://git.kernel.org/stable/c/c6980e8b1a86288167f34966fa5219031999b6f1","tags":["Patch"],"source":"416baaa9-dc9f-4396-8d5f-8c081fb06d67"},{"url":"https://git.kernel.org/stable/c/de42f86e2cf5028a97e74c25869d1a962b13c301","tags":["Patch"],"source":"416baaa9-dc9f-4396-8d5f-8c081fb06d67"},{"url":"https://git.kernel.org/stable/c/e76607442d5b73e1ba6768f501ef815bb58c2c0e","tags":["Patch"],"source":"416baaa9-dc9f-4396-8d5f-8c081fb06d67"},{"url":"https://cert-portal.siemens.com/productcert/html/ssa-784472.html","source":"0b142b55-0307-4c5a-b3c9-f314f3fb7c5e"}],"sources":{"nvd":"https://nvd.nist.gov/vuln/detail/CVE-2026-45842","epss":"https://www.first.org/epss/","kev":"https://www.cisa.gov/known-exploited-vulnerabilities-catalog","exploitdb":"https://www.exploit-db.com/"},"licence":"CC BY 4.0 — link back to the CVE Explorer if you publish the results; upstream data remains subject to its own terms."}