Fragnesia: New Linux kernel LPE bug was spawned by Dirty Frag patch (CVE-2026-46300)
Vulnerabilities mentionedAll →
| CVE | Vulnerability | CVSS | EPSS | Flags | Affected | Exposure | Published |
|---|---|---|---|---|---|---|---|
| CVE-2026-43284 | Linux kernel ESP-in-UDP decrypts in place over shared splice pages (CWE-123) CVE-2026-43284 is a write-what-where memory-safety flaw (CWE-123) in the Linux kernel's xfrm/ESP (IPsec) code: the IPv4/IPv6 UDP datagram send paths fail to mark pages spliced into a UDP skb with SKBFL_SHARED_FRAG when MSG_SPLICE_PAGES attaches pipe pages, so the ESP input path wrongly treats the packet as privately owned and decrypts it in place over memory the skb does not exclusively own. It is triggered when locally generated UDP traffic built from spliced pipe pages is processed by the ESP decryption path, typically in IPsec NAT-traversal (ESP-in-UDP, UDP port 4500) configurations; the in-place decrypt can corrupt or expose data still referenced by the pipe or other owners of those shared pages. A local, low-privileged attacker can thereby cause high-severity confidentiality, integrity, and availability impact that extends beyond the packet itself (CVSS 3.1: 8.8, scope changed); no remote or unauthenticated trigger is described. Any Linux system running a kernel with the vulnerable UDP splice and ESP-in-UDP paths is affected, most importantly IPsec VPN gateways and clients; the advisory lists no affected version ranges. No public proof-of-concept or confirmed in-the-wild exploitation is known (not on CISA KEV), but EPSS assigns a 93.2% probability of exploitation within 30 days (100th percentile), so patching should not be deferred. Do: Apply your distribution's kernel security update containing the xfrm/esp fix for CVE-2026-43284 and reboot into the patched kernel, prioritizing IPsec VPN gateways and clients that use ESP-in-UDP NAT-T (UDP/4500). Until patched, restrict untrusted local users from sending splice-based (MSG_SPLICE_PAGES) UDP traffic through IPsec-protected paths, or temporarily avoid ESP-in-UDP encapsulation where feasible. Verify the fix via your vendor's package changelog, as the advisory does not name specific fixed version numbers. | 8.8 | 93% |
| mass≈1M+ Linux installations carry the vulnerable code in default distro kernels; hundreds of thousands of hosts expose IPsec NAT-T (UDP/4500) in public internet… | ||
| CVE-2026-46300 | In the Linux kernel, the following vulnerability has been resolved: In the Linux kernel, the following vulnerability has been resolved: net: skbuff: preserve shared-frag marker during coalescing skb_try_coalesce() can attach paged frags from @from to @to. If @from has SKBFL_SHARED_FRAG set, the resulting @to skb can contain the same externally-owned or page-cache-backed frags, but the shared-frag marker is currently lost. That breaks the invariant relied on by later in-place writers. In particular, ESP input checks skb_has_shared_frag() before deciding whether an uncloned nonlinear skb can skip skb_cow_data(). If TCP receive coalescing has moved shared frags into an unmarked skb, ESP can see skb_has_shared_frag() as false and decrypt in place over page-cache backed frags. Propagate SKBFL_SHARED_FRAG when skb_try_coalesce() transfers paged frags. The tailroom copy path does not need the marker because it copies bytes into @to's linear data rather than transferring frag descriptors. NVD description · AI analysis pending | 7.8 | 9% |
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Full article454 words · extracted from helpnetsecurity.com · click to collapse
Researchers have found and disclosed yet another local privilege escalation (LPE) vulnerability in the Linux kernel: CVE-2026-46300, aka “Fragnesia”.
The flaw is in the same class of vulnerabilities as the recently disclosed Dirty Frag bug(s).
Like Dirty Frag, it affects the same Linux module (xfrm-ESP). In fact, according to Dirty Frag discoverer Hyunwoo Kim, Fragnesia was “accidentally activated” by the patch fixing one of the original Dirty Frag vulnerabilities (i.e., CVE-2026-43284).
CVE-2026-46300 explained
Fragnesia was discovered by William Bowling of Zellic.io, with the help of the company’s AI-agentic software auditing tool.
The research team published a short technical explainer and proof-of-concept exploit code.
As Wiz researchers helpfully explained, Fragnesia allows unprivileged local attackers to modify read-only file contents in the kernel page cache, and “through a deterministic page-cache corruption primitive,” achieve root privileges.
Patches and mitigations for Fragnesia
Like Copy Fail and Dirty Frag before it, Fragnesia is less of a risk for single-user workstations and single-tenant servers than for shared Linux hosts (where multiple users share a kernel), container clusters (where the page cache is shared across the host), CI runners and build farms, and cloud SaaS solutions running user code.
Linux admins should apply vendor kernel patches when they become available. In the meantime, they should disable/denylist or unload the vulnerable modules (for both Fragnesia and DirtyFrag: esp4, esp6, rxrpc) to mitigate the risk of exploitation.
Some Linux distributions have already relased kernel patches, namely AlmaLinux and CloudLinux.
“The exploit can modify legitimate system binaries (the public PoC overwrites /usr/bin/su) in the page cache as part of gaining root, so applying the mitigation alone is not enough on systems that may have been targeted before the mitigation was in place,” the CloudLinux team explained.
“After mitigating, drop the page cache to force a reload from disk [by running the following command: sudo sh -c “echo 3 > /proc/sys/vm/drop_caches”].”
Microsoft’s threat analysts also pointed out that exploitation is “not constrained to use the [/usr/bin/su] binary,” and that attackers “can modify any file readable by the user, including [/etc/passwd].”
They also added that there is currently no evidence pointing to in-the-wild exploitation of Fragnesia.
Copy Fail, on the other hand, has been added to CISA’s Known Exploited Vulnerabilities catalog earlier this month.
Kernel patches for Copy Fail are now widely available, but for a temporary mitigation admins can denylist or unload the algif_aead module.
UPDATE (May 18, 2026, 09:55 a.m. ET):
A variant of Dirty Frag and Fragnesia, called DirtyDecrypt (aka DirtyCBC), has been patched in the Linux kernel.
Researchers have published a PoC exploit.
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Text extracted automatically; images, tables and formatting may be missing. Original: https://www.helpnetsecurity.com/2026/05/14/fragnesia-cve-2026-46300-linux-lpe-vulnerability/