CVE-2026-45842
Received Received - Intake
Null pointer dereference in Linux kernel SLIP/CSLIP compression

Publication date: 2026-05-27

Last updated on: 2026-05-27

Assigner: kernel.org

Description
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'. In that case the allocation loop in slhc_init() is skipped, so comp->rstate stays NULL and comp->rslot_limit stays 0 (from the kzalloc of struct slcompress). The receive helpers do not defend against that configuration. slhc_uncompress() dereferences comp->rstate[x] when the VJ header carries an explicit connection ID, and slhc_remember() later assigns cs = &comp->rstate[...] after only comparing the packet's slot number to comp->rslot_limit. Because rslot_limit is 0, slot 0 passes the range check, and the code dereferences a NULL rstate. The configuration is reachable in-tree through PPP. PPPIOCSMAXCID stores its argument in a signed int, and (val >> 16) uses arithmetic shift. Passing 0xffff0000 therefore sign-extends to -1, so val2 + 1 is 0 and ppp_generic.c ends up calling slhc_init(0, 1). Because /dev/ppp open is gated by ns_capable(CAP_NET_ADMIN), the whole path is reachable from an unprivileged user namespace. Once the malformed VJ state is installed, any inbound VJ-compressed or VJ-uncompressed frame that selects slot 0 crashes the kernel in softirq context: Oops: general protection fault, probably for non-canonical address 0xdffffc0000000000: 0000 [#1] SMP KASAN NOPTI KASAN: null-ptr-deref in range [0x0000000000000000-0x0000000000000007] RIP: 0010:slhc_uncompress (drivers/net/slip/slhc.c:519) Call Trace: <TASK> ppp_receive_nonmp_frame (drivers/net/ppp/ppp_generic.c:2466) ppp_input (drivers/net/ppp/ppp_generic.c:2359) ppp_async_process (drivers/net/ppp/ppp_async.c:492) tasklet_action_common (kernel/softirq.c:926) handle_softirqs (kernel/softirq.c:623) run_ksoftirqd (kernel/softirq.c:1055) smpboot_thread_fn (kernel/smpboot.c:160) kthread (kernel/kthread.c:436) ret_from_fork (arch/x86/kernel/process.c:164) </TASK> Reject the receive side on such instances instead of touching rstate. slhc_uncompress() falls through to its existing 'bad' label, which bumps sls_i_error and enters the toss state. slhc_remember() mirrors that with an explicit sls_i_error increment followed by slhc_toss(); the sls_i_runt counter is not used here because a missing rstate is an internal configuration state, not a runt packet. The transmit path is unaffected: the only in-tree caller that picks rslots from userspace (ppp_generic.c) still supplies tslots >= 1, and slip.c always calls slhc_init(16, 16), so comp->tstate remains valid and slhc_compress() continues to work.
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Meta Information
Published
2026-05-27
Last Modified
2026-05-27
Generated
2026-05-27
AI Q&A
2026-05-27
EPSS Evaluated
N/A
NVD
CVE-2026-45842
EUVD
EUVD-2026-32168
Affected Vendors & Products
Showing 1 associated CPE
Vendor Product Version / Range
linux linux_kernel *
Helpful Resources
Exploitability
CWE
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KEV
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CWE ID Description
CWE-UNKNOWN
Attack-Flow Graph
AI Powered Q&A
Can you explain this vulnerability to me?

This vulnerability exists in the Linux kernel's slip network driver, specifically in the handling of Van Jacobson (VJ) header compression receive packets. The function slhc_init() accepts a configuration where the number of receive slots (rslots) is zero, meaning no receive compression. However, the receive helpers do not properly handle this case, leading to a NULL pointer dereference when processing packets with an explicit connection ID.

Because rslot_limit is zero, the code incorrectly allows slot 0 to pass a range check and then dereferences a NULL pointer, causing a kernel crash. This situation can be triggered through PPP (Point-to-Point Protocol) by passing a specially crafted argument that results in slhc_init(0, 1) being called. The vulnerability can be exploited from an unprivileged user namespace with CAP_NET_ADMIN capability, leading to a general protection fault and kernel crash.


How can this vulnerability impact me? :

This vulnerability can cause a denial of service by crashing the Linux kernel when it processes certain VJ-compressed or uncompressed frames that select slot 0. The crash occurs in softirq context due to a NULL pointer dereference, leading to a general protection fault.

An attacker with access to an unprivileged user namespace but with CAP_NET_ADMIN capability can trigger this vulnerability, potentially disrupting system availability by causing kernel panics or crashes.


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