NVD / CVE Program· CNA Linux

CVE-2026-63803: hdlc_ppp: sync per-proto timers before freeing hdlc state

Noroxi assessment

Priority: Monitor (action score 31/100)

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: 0.13% (FIRST EPSS).
Someone with local access to the system can trigger it. A low-privileged account is enough. No user action is required. No special conditions are required; it is repeatable.
Fixed version: Linux Linux 508a0139d3bf60f6a03d2fbfb63a89a9463d983a, 5a84398101bf9f11e84b176343e4e3ba83e668c0, 8308122bc9c065b1f376e081ed300129a2ac9545; azl3 kernel 6.6.143.1-1 on Azure Linux 3.0 6.6.150.1-1.
Mentioned 1 time in Turkish national cyber security advisories (siberguvenlik.gov.tr).

Low priority for now. Upgrade to Linux Linux 508a0139d3bf60f6a03d2fbfb63a89a9463d983a, 5a84398101bf9f11e84b176343e4e3ba83e668c0, 8308122bc9c065b1f376e081ed300129a2ac9545; azl3 kernel 6.6.143.1-1 on Azure Linux 3.0 6.6.150.1-1 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: hdlc_ppp: sync per-proto timers before freeing hdlc state Each PPP control protocol (LCP/IPCP/IPV6CP) embedded in struct ppp registers a timer via timer_setup(). That struct ppp is the hdlc->state allocation, which detach_hdlc_protocol() frees with kfree() in both teardown paths: unregister_hdlc_device() and the re-attach inside attach_hdlc_protocol(). The ppp proto never registered a .detach callback, so detach_hdlc_protocol() performs no timer synchronization before the kfree(). The only cancel, timer_delete(&proto->timer) in ppp_cp_event(), is partial (it does not wait for a running callback) and only runs on the ->CLOSED transition; ppp_stop()/ppp_close() do not sync either. A ppp_timer callback already executing (blocked on ppp->lock) survives the kfree and then dereferences proto->state / ppp->lock in freed memory, leading to a use-after-free. Fix this by adding a .detach helper that calls timer_shutdown_sync() on every per-proto timer. detach_hdlc_protocol() invokes proto->detach(dev) before kfree(hdlc->state), so timer_shutdown_sync() now runs on both free paths. timer_shutdown_sync() is used instead of timer_delete_sync() because the keepalive path re-arms the timer through add_timer()/mod_timer() and shutdown blocks any re-activation during teardown. Initialize the per-protocol timers in ppp_ioctl() when the protocol is attached, and remove the now-redundant timer_setup() from ppp_start(), so that the timers are initialized exactly once at attach time and ppp_timer_release() never operates on uninitialized timer_list structures. attach_hdlc_protocol() uses kmalloc() (not kzalloc), so struct ppp's protos[i].timer is uninitialized garbage until the first timer_setup(); without this init-at-attach, attaching the PPP protocol without ever bringing the device up would leave timer_shutdown_sync() operating on uninitialized memory in .detach. Moving the init out of ppp_start() (which only runs on NETDEV_UP) into the attach path makes the initialization unconditional and avoids initializing the same timer_list twice. This bug was found by static analysis.

HighCVSS 7.8 · v3.1—No exploit Fix available

Memory safety

Published: Jul 19, 2026
Updated: Oct 19, 2026
EPSS: 0.1% · 2th percentile
CWE: CWE-416

Report tools

JSON

Action score

Monitor

Low priority for now.

CVSS: 31 / 40 · 7.8 / 10
CISA KEV: 0 / 30 · Not listed
EPSS: 0 / 30 · 0.1%

CISA SSVC decision

Exploitation: none
Automatable: no
Technical impact: total

Vulnrichment: CISA's decision-tree inputs.

CNA vs NVD score

NVD: —
CNA · Linux: 7.8; 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

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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.

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Affected 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 kernel2.6.12.1 and later · before 5.10.261
linux linux kernel5.11 and later · before 5.15.211
linux linux kernel5.16 and later · before 6.1.177
linux linux kernel6.2 and later · before 6.6.144
linux linux kernel6.7 and later · before 6.12.95
linux linux kernel6.13 and later · before 6.18.38
linux linux kernel6.19 and later · before 7.1.3
linux linux kernel2.6.12

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
- 2.6.12affected
- 1da177e4c3f41524e886b7f1b8a0c1fc7321cac2 and later · before 86d80a231bde4cfb64bfbfbfffd83056fc93628faffected · git
- 1da177e4c3f41524e886b7f1b8a0c1fc7321cac2 and later · before 8308122bc9c065b1f376e081ed300129a2ac9545affected · git
- 1da177e4c3f41524e886b7f1b8a0c1fc7321cac2 and later · before ce8f9ddca0c9f217342a8b49efd309aa35b81a36affected · git
- 1da177e4c3f41524e886b7f1b8a0c1fc7321cac2 and later · before 508a0139d3bf60f6a03d2fbfb63a89a9463d983aaffected · git
- 1da177e4c3f41524e886b7f1b8a0c1fc7321cac2 and later · before c64dbef1c0fbd36f9530aa75112acdf6a6d3cfd8affected · git
- 1da177e4c3f41524e886b7f1b8a0c1fc7321cac2 and later · before 5a84398101bf9f11e84b176343e4e3ba83e668c0affected · git
- 1da177e4c3f41524e886b7f1b8a0c1fc7321cac2 and later · before a594debfd4e7ec39413647458907f689ef57fd2faffected · git
- 1da177e4c3f41524e886b7f1b8a0c1fc7321cac2 and later · before c78a4e41ab5ead6193ad8a2dd92e8906bae659faaffected · git
- before 2.6.12not affected · semver

Package-level exposure

OSV and GitHub Advisory data: ecosystem, package and range. SBOM matching uses this table.

Ecosystem	Package	Affected range	Fix
Debian:12	linux	before 6.1.177-1	6.1.177-1
Debian:13	linux	before 6.12.95-1	6.12.95-1
Debian:14	linux	before 7.1.3-1	7.1.3-1

Same product

linux: all records

Other highest-scoring records for the same primary product.

CVE-2026-31431crypto: algif_aead - Revert to operating out-of-placeKEV
90Now
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 KEV
89Now
CVE-2021-22555Heap Out-Of-Bounds Write in Netfilter IP6T_SO_SET_REPLACEKEV
85Now

Published before and after this one in the same product

← EarlierCVE-2026-63801Jul 19, 2026 · tipc: fix slab-use-after-free Read in tipc_aead_decrypt_done
35Monitor
← EarlierCVE-2026-63802Jul 19, 2026 · blk-cgroup: fix UAF in __blkcg_rstat_flush()
31Monitor
Later →CVE-2026-63804Jul 19, 2026 · gfs2: fix use-after-free in gfs2_qd_dealloc
31Monitor

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	508a0139d3bf60f6a03d2fbfb63a89a9463d983a	Vendor (CNA)
Linux Linux	5a84398101bf9f11e84b176343e4e3ba83e668c0	Vendor (CNA)
Linux Linux	8308122bc9c065b1f376e081ed300129a2ac9545	Vendor (CNA)
Linux Linux	86d80a231bde4cfb64bfbfbfffd83056fc93628f	Vendor (CNA)
Linux Linux	a594debfd4e7ec39413647458907f689ef57fd2f	Vendor (CNA)
Linux Linux	c64dbef1c0fbd36f9530aa75112acdf6a6d3cfd8	Vendor (CNA)
Linux Linux	c78a4e41ab5ead6193ad8a2dd92e8906bae659fa	Vendor (CNA)
Linux Linux	ce8f9ddca0c9f217342a8b49efd309aa35b81a36	Vendor (CNA)
azl3 kernel 6.6.143.1-1 on Azure Linux 3.0	6.6.150.1-1 · CBL-Mariner Releases	Microsoft (MSRC)
debian:linux	6.1.177-1 · Debian:12	Package registry (OSV)

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.

EPSS, last 120 days

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 researchers

Finders, 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).

National notice (Türkiye Cybersecurity Directorate / USOM)

Official security notices citing this record; remediation advice is on the agency's page.

TR-26-0576 · Jul 20, 2026(Linux Kernel Güvenlik Bildirimi)

All national notices →

Technical details

Attack conditions

Someone with local access to the system can trigger it.
A low-privileged account is enough.
No user action is required.
No special conditions are required; it is repeatable.

If successful

Confidentiality: high · data can be read
Integrity: high · data or configuration can be modified
Availability: high · the service can be disrupted

Attack vector: Local
Attack complexity: Low
Privileges required: Low
User interaction: None
Scope: Unchanged
Confidentiality impact: High
Integrity impact: High
Availability impact: High

Weakness class (CWE)

CWE-416 · Use After Free

CVSS vector

CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H

nvd-secondary

Root cause

After a memory region is freed, another reference pointing to it is still used. By then, the same region may have been allocated for different data.

The bug in code

The whole CWE-416 class

A representative example of this vulnerability class. Not the vendor's source code; it shows the faulty pattern and its fix.

Vulnerable

1free(dev->buf);
2/* ... another thread is still running ... */
3process(dev->buf);

Fixed

1lock(&dev->lock);
2free(dev->buf);
3dev->buf = NULL;
4unlock(&dev->lock);

Attack context

MITRE CAPEC attack patterns and ATT&CK techniques for this weakness class (CWE). A starting point for detection rules and threat hunting.

MITRE has no CAPEC/ATT&CK mapping for this CWE.

Change log

SSVC exploitation— → noneOct 16, 2026, 5:07 PM UTC
Fix✗ → ✓Sep 28, 2026, 10:09 PM UTC

For records you follow, these changes also arrive as notifications. →

References

git.kernel.org/stable/c/508a0139d3bf60f6a03d2fbfb63a89a9463d983a

Show all references (7 more)

Vendor advisories and official records. Exploit/PoC links are deliberately left out.

All records