CVE-2024-56644 — net/ipv6: release expired exception dst cached in socket
In the Linux kernel, the following vulnerability has been resolved: net/ipv6: release expired exception dst cached in socket Dst objects get leaked in ip6_negative_advice() when this function is executed for an expired IPv6 route located in the exception table. There are several conditions that must be fulfilled for the leak to occur: * an ICMPv6 packet indicating a change of the MTU for the path is received, resulting in an exception dst being created * a TCP connection that uses the exception dst for routing packets must start timing out so that TCP begins retransmissions * after the exception dst expires, the FIB6 garbage collector must not run before TCP executes ip6_negative_advice() for the expired exception dst When TCP executes ip6_negative_advice() for an exception dst that has expired and if no other socket holds a reference to the exception dst, the refcount of the exception dst is 2, which corresponds to the increment made by dst_init() and the increment made by the TCP socket for which the connection is timing out. The refcount made by the socket is never released. The refcount of the dst is decremented in sk_dst_reset() but that decrement is counteracted by a dst_hold() intentionally placed just before the sk_dst_reset() in ip6_negative_advice(). After ip6_negative_advice() has finished, there is no other object tied to the dst. The socket lost its reference stored in sk_dst_cache and the dst is no longer in the exception table. The exception dst becomes a leaked object. As a result of this dst leak, an unbalanced refcount is reported for the loopback device of a net namespace being destroyed under kernels that do not contain e5f80fcf869a ("ipv6: give an IPv6 dev to blackhole_netdev"): unregister_netdevice: waiting for lo to become free. Usage count = 2 Fix the dst leak by removing the dst_hold() in ip6_negative_advice(). The patch that introduced the dst_hold() in ip6_negative_advice() was 92f1655aa2b22 ("net: fix __dst_negative_advice() race"). But 92f1655aa2b22 merely refactored the code with regards to the dst refcount so the issue was present even before 92f1655aa2b22. The bug was introduced in 54c1a859efd9f ("ipv6: Don't drop cache route entry unless timer actually expired.") where the expired cached route is deleted and the sk_dst_cache member of the socket is set to NULL by calling dst_negative_advice() but the refcount belonging to the socket is left unbalanced. The IPv4 version - ipv4_negative_advice() - is not affected by this bug. When the TCP connection times out ipv4_negative_advice() merely resets the sk_dst_cache of the socket while decrementing the refcount of the exception dst.
Who exploits it and how urgent it is
A 0–100 score combining confirmed exploitation, ransomware and APT use, public exploits, EPSS and severity.
How the score was calculated
- EPSS 0.7% (30-day exploitation probability)+8
- Technical severity (medium)+3
- Automatable exploitation (SSVC)+3
The score orders the patch queue; it does not replace your asset context (internet exposure, criticality, compensating controls).
Triage
Is it exploited, how likely is exploitation, what does it touch, and how severe do the sources call it.
CISA SSVC assessment CISA
Three decision points CISA publishes for the CVEs it assesses (SSVC 2.0.3). A stakeholder decision, not a severity score.
Remediation
Fixes and mitigations documented by the sources — linked to the original advisory.
- Documented patch — git.kernel.org (NIST National Vulnerability Database)
- Documented patch — git.kernel.org (NIST National Vulnerability Database)
- Documented patch — git.kernel.org (NIST National Vulnerability Database)
- Documented patch — git.kernel.org (NIST National Vulnerability Database)
- Documented patch — git.kernel.org (NIST National Vulnerability Database)
- Documented patch — git.kernel.org (NIST National Vulnerability Database)
- Documented patch — git.kernel.org (NIST National Vulnerability Database)
First 24 hours
Ordered from the record’s own fields — exposure first, because you cannot patch what you have not found. A rule-generated starting point.
- Identify exposed assets running the affected vendor/product/version combinations (Debian Debian Linux, Linux Linux, Linux Linux Kernel).
- Apply the fixed version or the patch documented under Remediation.
- Search available logs for exploit probes, errors and authentication anomalies.
Affected scope
Vendor, product and versions as the sources word them.
| Vendor | Product | Versions | Status | Source |
|---|---|---|---|---|
| Debian | Debian Linux | version 11.0 | Vulnerable | NIST National Vulnerability Database |
| Linux | Linux |
version 2.6.34≥ 2.6.33.2 and < 2.6.34version 9c93e9c757c7d3d96027a06b9b4c4e37ca87ded7≥ 54c1a859efd9fd6cda05bc700315ba2519c14eba and < 3301ab7d5aeb0fe270f73a3d4810c9d1b6a9f045≥ 54c1a859efd9fd6cda05bc700315ba2519c14eba and < 8b591bd522b71c42a82898290e35d32b482047e4≥ 54c1a859efd9fd6cda05bc700315ba2519c14eba and < f43d12fd0fa8ee5b9caf8a3927e10d06431764d2≥ 54c1a859efd9fd6cda05bc700315ba2519c14eba and < 535add1e9f274502209cb997801208bbe1ae6c6f≥ 54c1a859efd9fd6cda05bc700315ba2519c14eba and < 0b8903e6c881f72c6849d4952de742c656eb5ab9 and 2 more≥ 54c1a859efd9fd6cda05bc700315ba2519c14eba and < b90d061345bb8cd51fece561a800bae1c95448a6≥ 54c1a859efd9fd6cda05bc700315ba2519c14eba and < a95808252e8acc0123bacd2dff8b9af10bc145b7 |
Vulnerable | CVE Program (cve.org) e CISA ADP |
| Linux | Linux Kernel |
version 2.6.34-rc6version 6.13-rc1version 2.6.34-rc7version 2.6.34-rc5version 2.6.34-rc4version 2.6.34-rc3version 2.6.34≥ 6.7 and < 6.12.5 and 6 more≥ 6.2 and < 6.6.66≥ 5.16 and < 6.1.120≥ 5.11 and < 5.15.174≥ 5.5 and < 5.10.231≥ 2.6.34.1 and < 5.4.287≥ 2.6.33.2 and < 2.6.34 |
Vulnerable | NIST National Vulnerability Database |
Attack characteristics
The CVSS vector, decoded. It describes the attack, not your exposure to it.
Every base score collected
Sources score independently and may disagree; each row says who scored it and under which version.
| Score | Version | Severity | Expl. | Impact | Scored by |
|---|---|---|---|---|---|
| 7.5 | CVSS 3.1 | High | 3.9 | 3.6 | 416baaa9-dc9f-4396-8d5f-8c081fb06d67 via NIST National Vulnerability Database |
| 7.5 | CVSS 3.1 | High | — | — | Linux via CVE Program (cve.org) e CISA ADP |
| 5.5 | CVSS 3.1 | Medium | 1.8 | 3.6 | nvd@nist.gov via NIST National Vulnerability Database |
| 5.5 | CVSS 3.1 | Medium | — | — | GitHub, Inc. via GitHub Security Advisories |
CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H (score shown at the top: nvd@nist.gov) Detection
Read off the CVSS vector and the weakness class. Starting points, not tested rules.
- Local/physical vector: focus on endpoint telemetry (EDR) from affected hosts.
Timeline
What happened to this CVE, newest first.
- 2026
- SSVC assessment updated
- Affected products added · linux/linux
- Record published
- Fix documented
- Affected products added · linux/linux kernel, debian/debian linux
- CVSS changed · 5.5
- Source status changed · → Modified
- Record created in this database
- 2024
- CVE published
Source activity
Repeated readings are counted rather than listed.
- 2× References added · Oct 14, 2026 – Oct 14, 2026
- 1× Official description updated · Oct 14, 2026 – Oct 14, 2026
References
13 on the record
- git.kernel.org/stable/c/3301ab7d5aeb0fe270f73a3d4810c9d1b6a9f045
- git.kernel.org/stable/c/8b591bd522b71c42a82898290e35d32b482047e4
- git.kernel.org/stable/c/b90d061345bb8cd51fece561a800bae1c95448a6
- git.kernel.org/stable/c/535add1e9f274502209cb997801208bbe1ae6c6f
- git.kernel.org/stable/c/f43d12fd0fa8ee5b9caf8a3927e10d06431764d2
- git.kernel.org/stable/c/a95808252e8acc0123bacd2dff8b9af10bc145b7
- git.kernel.org/stable/c/0b8903e6c881f72c6849d4952de742c656eb5ab9
- lists.debian.org/debian-lts-announce/2025/03/msg00001.html
- cert-portal.siemens.com/productcert/html/ssa-398330.html
- cert-portal.siemens.com/productcert/html/ssa-355557.html
- github.com/advisories/GHSA-4cgh-427p-hh6m
- nvd.nist.gov/vuln/detail/CVE-2024-56644
- lists.debian.org/debian-lts-announce/2025/03/msg00002.html
Elsewhere on this site
Related CVEs (same products)
- Critical CVE-2026-99999 ipv4: validate checksum_start before completing checksum 9h
- Unknown CVE-2026-98432 ipv4: free inet_opt and ireq_opt after an RCU grace period 9h
- Unknown CVE-2026-98431 RDMA/uverbs: Fix mmap_lock/disassociation_lock circular dependency 1d
- Unknown CVE-2026-98430 RDMA/efa: Keep admin queues alive while IRQ is registered 1d
- Unknown CVE-2026-98429 RDMA/efa: Keep EQ resources alive while IRQ is registered 1d
- Unknown CVE-2026-98428 ALSA: usb: 6fire: Avoid embedded URBs 1d
Not in any source we poll
Listed rather than left blank: an empty field and an unmeasured one look identical on screen, and only one is a reason to look elsewhere.
- No CWE classification.
- No confirmed IOCs, IP addresses, domains, file hashes, or malware artifacts supplied.
- No organization-specific asset inventory, compensating-control status, or patch deployment evidence supplied.
- No exploit packet captures, log samples, or incident case IDs supplied.
Answered from this record
Text assembled only from the fields above — no additional claims.
What should defenders know first?
CVE-2024-56644 is "net/ipv6: release expired exception dst cached in socket", rated Medium. It affects Debian Linux (Debian); versions are in the scope table. It is not in CISA KEV, which does not rule out exploitation. CVSS 5.5 describes technical severity. EPSS 0.70% estimates the probability of exploitation in 30 days; neither replaces your asset context. First verify whether exposed or business-critical assets run the affected versions, apply vendor fixes or mitigations, and preserve logs for review.
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