CVE-2026-23455: netfilter: nf_conntrack_h323: check for zero length in DecodeQ931()
Noroxi assessment
Priority: Monitor (action score 36/100)
- The sources we track (CISA KEV, Exploit-DB, Metasploit, Nuclei, GitHub) show no public exploit code or exploitation in the wild.
- Probability of exploitation in the next 30 days: 1.5% (FIRST EPSS); higher than 75.7% of all records.
- Anyone who can reach it over the internet can trigger it. No account or password is required. No user action is required. No special conditions are required; it is repeatable.
- According to CISA the attack is automatable: targets can be found by mass scanning.
- Fixed version: Linux Linux 2121f5fbe88daff0f1fc5bc47d359426c74b86b0, 495e97af9e7249ee02b72bb1d0848a6efc3700f4, 633e8f87dad32263f6a57dccdb873f042c062111.
Low priority for now. Upgrade to Linux Linux 2121f5fbe88daff0f1fc5bc47d359426c74b86b0, 495e97af9e7249ee02b72bb1d0848a6efc3700f4, 633e8f87dad32263f6a57dccdb873f042c062111 or later.
Generated automatically from the record's data: CVSS (NVD and CNA), CISA KEV and SSVC, FIRST EPSS, exploit sources, fixed versions. How we calculate it
Primary sources: NVD · CVE.org · FIRST EPSS
In the Linux kernel, the following vulnerability has been resolved: netfilter: nf_conntrack_h323: check for zero length in DecodeQ931() In DecodeQ931(), the UserUserIE code path reads a 16-bit length from the packet, then decrements it by 1 to skip the protocol discriminator byte before passing it to DecodeH323_UserInformation(). If the encoded length is 0, the decrement wraps to -1, which is then passed as a large value to the decoder, leading to an out-of-bounds read. Add a check to ensure len is positive after the decrement.
- BDU:2026-12238
- ALSA-2026:21556
- ALSA-2026:21557
- ALSA-2026:21706
- ALSA-2026:21745
- RHSA-2026:21556
- RHSA-2026:21557
- RHSA-2026:21706
- RHSA-2026:21745
- RHSA-2026:25218
- RHSA-2026:26462
- RHSA-2026:26515
- RHSA-2026:27713
- RHSA-2026:33899
- RHSA-2026:35844
- RHSA-2026:35863
- RHSA-2026:35896
- RHSA-2026:41236
- RHSA-2026:55445
- RLSA-2026:21556
- Published
- Apr 3, 2026
- Updated
- Oct 19, 2026
- EPSS
- 1.5% · 75th percentile
- CWE
- CWE-125
Report tools
Action score
36
Monitor
Low priority for now.
- CVSS
- 36 / 40 · 9.1 / 10
- CISA KEV
- 0 / 30 · Not listed
- EPSS
- 0 / 30 · 1.5%
CISA SSVC decision
- Exploitation
- none
- Automatable
- yes
- Technical impact
- partial
Vulnrichment: CISA's decision-tree inputs.
CNA vs NVD score
- NVD
- —
- CNA · Linux
- 9.1
- NVD has not scored this yet; the score shown is the CNA’s.
The score given by the assigning authority versus NVD’s independent score. A gap means the severity is contested.
Get told when this record changes
- Not in KEV: no record of exploitation in the wild
- No public exploit code on record
- A fix has been released
If any of these changes, we'll tell you in the daily email digest.
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Noroxi analysis
What does it mean in your environment?
The assessment above is generated automatically from the record's data; it doesn't know your environment. Our team verifies on your systems whether this vulnerability is actually exploitable and which mitigation is enough.
We use this product, ask for helpAffected systems
Is your version affected?
Pick the product and type the version you run. It's compared with this record's version ranges in your browser; the version isn't sent anywhere.
| Vendor | Product | CPE |
|---|---|---|
| linux | linux kernel | cpe:2.3:o:linux:linux_kernel |
Affected versions
NVD version ranges (for catalog products). Add the product to your stack with a version and matching uses these.
- linux linux kernel2.6.17 and later · before 5.10.253
- linux linux kernel5.11 and later · before 5.15.203
- linux linux kernel5.16 and later · before 6.1.167
- linux linux kernel6.2 and later · before 6.6.130
- linux linux kernel6.7 and later · before 6.12.78
- linux linux kernel6.13 and later · before 6.18.20
- linux linux kernel6.19 and later · before 6.19.10
- linux linux kernel7.0
Versions reported by the vendor
Affected version ranges reported by the assigning authority (Linux). Independent of NVD's CPE analysis and usually ahead of it.
Linux Linux
- 2.6.17affected
- 5e35941d990123f155b02d5663e51a24f816b6f3 and later · before 2121f5fbe88daff0f1fc5bc47d359426c74b86b0affected · git
- 5e35941d990123f155b02d5663e51a24f816b6f3 and later · before 65fa92f79677858b14b9e4b7275f26639afe2710affected · git
- 5e35941d990123f155b02d5663e51a24f816b6f3 and later · before 495e97af9e7249ee02b72bb1d0848a6efc3700f4affected · git
- 5e35941d990123f155b02d5663e51a24f816b6f3 and later · before f5e4f4e4cdb75ec36802059a94195a31f193da60affected · git
- 5e35941d990123f155b02d5663e51a24f816b6f3 and later · before 633e8f87dad32263f6a57dccdb873f042c062111affected · git
- 5e35941d990123f155b02d5663e51a24f816b6f3 and later · before 9d00fe7d6d7c5b5f1065a6e042b54f2e44bd6df8affected · git
- 5e35941d990123f155b02d5663e51a24f816b6f3 and later · before b652b05d51003ac074b912684f9ec7486231717baffected · git
- 5e35941d990123f155b02d5663e51a24f816b6f3 and later · before f173d0f4c0f689173f8cdac79991043a4a89bf66affected · git
- before 2.6.17not affected · semver
Package-level exposure
OSV and GitHub Advisory data: ecosystem, package and range. SBOM matching uses this table.
| Ecosystem | Package | Affected range | Fix |
|---|---|---|---|
| AlmaLinux:10 | kernel | before 6.12.0-211.18.1.el10_2 | 6.12.0-211.18.1.el10_2 |
| AlmaLinux:10 | kernel-64k | before 6.12.0-211.18.1.el10_2 | 6.12.0-211.18.1.el10_2 |
| AlmaLinux:10 | kernel-64k-core | before 6.12.0-211.18.1.el10_2 | 6.12.0-211.18.1.el10_2 |
| AlmaLinux:10 | kernel-64k-debug | before 6.12.0-211.18.1.el10_2 | 6.12.0-211.18.1.el10_2 |
| AlmaLinux:10 | kernel-64k-debug-core | before 6.12.0-211.18.1.el10_2 | 6.12.0-211.18.1.el10_2 |
| AlmaLinux:10 | kernel-64k-debug-devel | before 6.12.0-211.18.1.el10_2 | 6.12.0-211.18.1.el10_2 |
| AlmaLinux:10 | kernel-64k-debug-devel-matched | before 6.12.0-211.18.1.el10_2 | 6.12.0-211.18.1.el10_2 |
| AlmaLinux:10 | kernel-64k-debug-modules | before 6.12.0-211.18.1.el10_2 | 6.12.0-211.18.1.el10_2 |
| AlmaLinux:10 | kernel-64k-debug-modules-core | before 6.12.0-211.18.1.el10_2 | 6.12.0-211.18.1.el10_2 |
| AlmaLinux:10 | kernel-64k-debug-modules-extra | before 6.12.0-211.18.1.el10_2 | 6.12.0-211.18.1.el10_2 |
| AlmaLinux:10 | kernel-64k-devel | before 6.12.0-211.18.1.el10_2 | 6.12.0-211.18.1.el10_2 |
| AlmaLinux:10 | kernel-64k-devel-matched | before 6.12.0-211.18.1.el10_2 | 6.12.0-211.18.1.el10_2 |
| AlmaLinux:10 | kernel-64k-modules | before 6.12.0-211.18.1.el10_2 | 6.12.0-211.18.1.el10_2 |
| AlmaLinux:10 | kernel-64k-modules-core | before 6.12.0-211.18.1.el10_2 | 6.12.0-211.18.1.el10_2 |
| AlmaLinux:10 | kernel-64k-modules-extra | before 6.12.0-211.18.1.el10_2 | 6.12.0-211.18.1.el10_2 |
| AlmaLinux:10 | kernel-abi-stablelists | before 6.12.0-211.18.1.el10_2 | 6.12.0-211.18.1.el10_2 |
| AlmaLinux:10 | kernel-core | before 6.12.0-211.18.1.el10_2 | 6.12.0-211.18.1.el10_2 |
| AlmaLinux:10 | kernel-cross-headers | before 6.12.0-211.18.1.el10_2 | 6.12.0-211.18.1.el10_2 |
| AlmaLinux:10 | kernel-debug | before 6.12.0-211.18.1.el10_2 | 6.12.0-211.18.1.el10_2 |
| AlmaLinux:10 | kernel-debug-core | before 6.12.0-211.18.1.el10_2 | 6.12.0-211.18.1.el10_2 |
| AlmaLinux:10 | kernel-debug-devel | before 6.12.0-211.18.1.el10_2 | 6.12.0-211.18.1.el10_2 |
| AlmaLinux:10 | kernel-debug-devel-matched | before 6.12.0-211.18.1.el10_2 | 6.12.0-211.18.1.el10_2 |
| AlmaLinux:10 | kernel-debug-modules | before 6.12.0-211.18.1.el10_2 | 6.12.0-211.18.1.el10_2 |
| AlmaLinux:10 | kernel-debug-modules-core | before 6.12.0-211.18.1.el10_2 | 6.12.0-211.18.1.el10_2 |
+96
Same product
linux: all recordsOther highest-scoring records for the same primary product.
- CVE-2026-31431crypto: algif_aead - Revert to operating out-of-placeKEV90Now
- CVE-2022-0847A flaw was found in the way the "flags" member of the new pipe buffer structure was lacking proper initialization in copy_page_to_iter_pipe KEV89Now
- CVE-2021-22555Heap Out-Of-Bounds Write in Netfilter IP6T_SO_SET_REPLACEKEV85Now
Published before and after this one in the same product
- ← EarlierCVE-2026-23452Apr 3, 2026 · PM: runtime: Fix a race condition related to device removal18Monitor
- ← EarlierCVE-2026-23454Apr 3, 2026 · net: mana: fix use-after-free in mana_hwc_destroy_channel() by reordering teardown28Monitor
- Later →CVE-2026-23456Apr 3, 2026 · netfilter: nf_conntrack_h323: fix OOB read in decode_int() CONS case32Monitor
Remediation
Which version to upgrade to
Fix versions compiled from the vendor, package registries and Microsoft. Verify the vendor's note before upgrading.
| Product / package | Fixed version | Source |
|---|---|---|
| Linux Linux | 2121f5fbe88daff0f1fc5bc47d359426c74b86b0 | Vendor (CNA) |
| Linux Linux | 495e97af9e7249ee02b72bb1d0848a6efc3700f4 | Vendor (CNA) |
| Linux Linux | 633e8f87dad32263f6a57dccdb873f042c062111 | Vendor (CNA) |
| Linux Linux | 65fa92f79677858b14b9e4b7275f26639afe2710 | Vendor (CNA) |
| Linux Linux | 9d00fe7d6d7c5b5f1065a6e042b54f2e44bd6df8 | Vendor (CNA) |
| Linux Linux | b652b05d51003ac074b912684f9ec7486231717b | Vendor (CNA) |
| Linux Linux | f173d0f4c0f689173f8cdac79991043a4a89bf66 | Vendor (CNA) |
| Linux Linux | f5e4f4e4cdb75ec36802059a94195a31f193da60 | Vendor (CNA) |
| almalinux:kernel | 5.14.0-687.12.1.el9_8 · AlmaLinux:9 | Package registry (OSV) |
| almalinux:kernel-64k | 5.14.0-687.12.1.el9_8 · AlmaLinux:9 | Package registry (OSV) |
| almalinux:kernel-64k-core | 5.14.0-687.12.1.el9_8 · AlmaLinux:9 | Package registry (OSV) |
| almalinux:kernel-64k-debug | 5.14.0-687.12.1.el9_8 · AlmaLinux:9 | Package registry (OSV) |
| almalinux:kernel-64k-debug-core | 5.14.0-687.12.1.el9_8 · AlmaLinux:9 | Package registry (OSV) |
| almalinux:kernel-64k-debug-devel | 5.14.0-687.12.1.el9_8 · AlmaLinux:9 | Package registry (OSV) |
| almalinux:kernel-64k-debug-devel-matched | 5.14.0-687.12.1.el9_8 · AlmaLinux:9 | Package registry (OSV) |
| almalinux:kernel-64k-debug-modules | 5.14.0-687.12.1.el9_8 · AlmaLinux:9 | Package registry (OSV) |
| almalinux:kernel-64k-debug-modules-core | 5.14.0-687.12.1.el9_8 · AlmaLinux:9 | Package registry (OSV) |
| almalinux:kernel-64k-debug-modules-extra | 5.14.0-687.12.1.el9_8 · AlmaLinux:9 | Package registry (OSV) |
| almalinux:kernel-64k-devel | 5.14.0-687.12.1.el9_8 · AlmaLinux:9 | Package registry (OSV) |
| almalinux:kernel-64k-devel-matched | 5.14.0-687.12.1.el9_8 · AlmaLinux:9 | Package registry (OSV) |
| debian:linux | 6.1.170-1 · Debian:12 | Package registry (OSV) |
| red hat:kernel-64k-debug-debuginfo | 0:5.14.0-687.12.1.el9_8 · Red Hat:enterprise_linux:9::appstream | Package registry (OSV) |
| red hat:kernel-64k-debug-devel | 0:5.14.0-687.12.1.el9_8 · Red Hat:enterprise_linux:9::appstream | Package registry (OSV) |
| red hat:kernel-64k-debug-devel-matched | 0:5.14.0-687.12.1.el9_8 · Red Hat:enterprise_linux:9::appstream | Package registry (OSV) |
| red hat:kernel-64k-debuginfo | 0:5.14.0-687.12.1.el9_8 · Red Hat:enterprise_linux:9::appstream | Package registry (OSV) |
| red hat:kernel-64k-devel | 0:5.14.0-687.12.1.el9_8 · Red Hat:enterprise_linux:9::appstream | Package registry (OSV) |
| red hat:kernel-64k-devel-matched | 0:5.14.0-687.12.1.el9_8 · Red Hat:enterprise_linux:9::appstream | Package registry (OSV) |
| red hat:kernel-debug-debuginfo | 0:5.14.0-687.12.1.el9_8 · Red Hat:enterprise_linux:9::appstream | Package registry (OSV) |
| red hat:kernel-debug-devel | 0:5.14.0-687.12.1.el9_8 · Red Hat:enterprise_linux:9::appstream | Package registry (OSV) |
| red hat:kernel-debug-devel-matched | 0:5.14.0-687.12.1.el9_8 · Red Hat:enterprise_linux:9::appstream | Package registry (OSV) |
+5
Exploit status
No known public exploit
No public exploit has been observed yet. That doesn't mean you're safe, only that the bar is a little higher.
Research context
For pentesters and researchers: attack profile, score disagreement, timeline, patch commits, credits, variant and chain candidates, bug bounty scope. All derived from existing data; no exploit code.
Timeline
From publication to today: proof of concept, Metasploit module, CISA KEV and fix record. Dates are as reported by the sources.
No dated events beyond publication.
FIRST EPSS daily score; only changes of 0.01 or more are recorded (step chart).
Patch and commit links
Commit, PR and diff links among the references. A starting point for patch-diffing and variant hunting; fixes, not exploits.
No commit or PR link among the references.
Credits
All researchersFinders, reporters and analysts named in the CNA record. Click a name for that researcher’s other records.
No credits in the CNA record.
Variant candidates
Same product, same weakness class, within 18 months. If the patch missed the root cause, the sibling bug is here.
No nightly-computed relations.
Chain candidates
An authentication bypass and a privilege-requiring bug in the same product, published close together: combined they may become an unauthenticated path.
—
Bug bounty scope
No known public program.
Source: bounty-targets-data (public HackerOne, Bugcrowd, Intigriti, YesWeHack listings).
Technical details
Attack conditions
- Anyone who can reach it over the internet can trigger it.
- No account or password is required.
- No user action is required.
- No special conditions are required; it is repeatable.
If successful
- Confidentiality
- high · data can be read
- Integrity
- none
- Availability
- high · the service can be disrupted
- Attack vector
- Network
- Attack complexity
- Low
- Privileges required
- None
- User interaction
- None
- Scope
- Unchanged
- Confidentiality impact
- High
- Integrity impact
- None
- Availability impact
- High
Weakness class (CWE)
CWE-125 · Out-of-bounds ReadCVSS vector
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:N/A:H
nvd-secondary
Attack context
MITRE CAPEC attack patterns and ATT&CK techniques for this weakness class (CWE). A starting point for detection rules and threat hunting.
Attack patterns (CAPEC)
ATT&CK techniques
—
Change log
- SSVC exploitation— → none
- Fix✗ → ✓
For records you follow, these changes also arrive as notifications. →
References
Show all references (10 more)Show less
- git.kernel.org/stable/c/495e97af9e7249ee02b72bb1d0848a6efc3700f4
- git.kernel.org/stable/c/633e8f87dad32263f6a57dccdb873f042c062111
- git.kernel.org/stable/c/65fa92f79677858b14b9e4b7275f26639afe2710
- git.kernel.org/stable/c/9d00fe7d6d7c5b5f1065a6e042b54f2e44bd6df8
- git.kernel.org/stable/c/b652b05d51003ac074b912684f9ec7486231717b
- git.kernel.org/stable/c/f173d0f4c0f689173f8cdac79991043a4a89bf66
- git.kernel.org/stable/c/f5e4f4e4cdb75ec36802059a94195a31f193da60
- cert-portal.siemens.com/productcert/html/ssa-019113.html
- cert-portal.siemens.com/productcert/html/ssa-082556.html
- cert-portal.siemens.com/productcert/html/ssa-457936.html
Vendor advisories and official records. Exploit/PoC links are deliberately left out.