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Reported by 5 outlets

Fragnesia — new Dirty Frag-class Linux kernel LPE (CVE-2026-46300), PoC public, patches rolling out

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Why this score
Breadth
2.00 / 2.0 · 5 sources
Authority
1.80 / 2.0 · best outlet weight
Severity
4.40 / 5.0 · CVSS + KEV signals
Velocity
0.00 / 2.0 · updates in 48h
Pickup speed
0.50 / 0.6 · time to second source
Recency
× 0.00 temporal multiplier
Community
+ 0.00 / 1.5 · reddit signal
Score
0.0 / 10 = base × recency + community
bleepingcomputer.comaccess.redhat.comlists.openwall.nettenable.comgithub.com CVE-2026-31431CVE-2026-43284CVE-2026-43500CVE-2026-46300 KEV desk first seen 153d ago

Desk analysis

Fragnesia (CVE-2026-46300) is a deterministic local privilege escalation in the Linux kernel XFRM ESP-in-TCP subsystem discovered by William Bowling (Zellic/V12). It is not an independent bug but a regression introduced by the Dirty Frag fix (CVE-2026-43284): the patch changed how skb_try_coalesce() propagates SKBFL_SHARED_FRAG, which accidentally drops the shared-frag marker along the espintcp ULP-transition path. The result is a 192-byte per trigger AES-GCM keystream XOR directly into the page cache of any user-readable file - no race condition required. The public PoC overwrites the first 192 bytes of /usr/bin/su in the page cache with a root-shell ELF stub; on-disk binary is untouched and a reboot clears the modification. All kernels before the 13 May 2026 patch are affected, including the confirmed working target Ubuntu 6.8.0-111-generic.

The exposure profile is worse than a routine LPE because it is a regression of the very patch meant to stop Dirty Frag. Organizations that applied kernel updates for CVE-2026-43284 without also blacklisting esp4, esp6, and rxrpc remain fully vulnerable - the event timeline notes AlmaLinux and Fedora patched by 15 May while Ubuntu, Debian, RHEL, and openSUSE stayed exposed. The exploit requires only unprivileged user+network namespace access (CAP_NET_ADMIN from unshare) unless kernel.apparmor_restrict_unprivileged_userns is enforced, which means multi-tenant or container-escape scenarios are realistic. With a public PoC available, deterministic exploitation, and a third universal Linux LPE in two weeks, this is not background noise - it is an active, near-zero-skill root vector against any unpatched Linux server reachable via SSH or web shell.

Defenders should apply the 13 May 2026 kernel patch immediately, then enforce the module blacklist: rmmod esp4 esp6 rxrpc and install /etc/modprobe.d/dirtyfrag.conf with install lines for all three. On Ubuntu specifically disable the namespace restriction only after confirming the blacklist is loaded, and run echo 1 | tee /proc/sys/vm/drop_caches after any suspected exploitation because the injected stub in /usr/bin/su page cache persists until eviction or reboot. Hunt for namespace creation followed by XFRM SA installation (NETLINK_XFRM with AES-128-GCM SPI 0x100) in audit logs, and monitor for unexpected executions of /usr/bin/su spawning root shells.

Watch for the patch rollout to Ubuntu, Debian, RHEL, and openSUSE - the 15 May update event shows these distributions were still vulnerable - and watch for any in-the-wild telemetry confirming exploitation beyond the public PoC. If a CISA KEV listing appears, treat as confirmed active exploitation and accelerate patching timelines.

Timeline

  1. original reporting

    Fragnesia — new Dirty Frag-class Linux kernel LPE (CVE-2026-46300), PoC public, patches rolling out

    bleepingcomputer.com · 153d ago · May 14th, 2026

    Zellic's head of assurance William Bowling has disclosed Fragnesia (CVE-2026-46300), a separate logic bug in the Linux XFRM ESP-in-TCP subsystem that allows unprivileged local attackers to gain root by writing arbitrary bytes into the kernel page cache of read-only files. Like Dirty Frag (CVE-2026-43284/CVE-2026-43500), it requires no race condition and is deterministic. The proof-of-concept corrupts /usr/bin/su page cache memory to achieve a root shell. Fragnesia is the third universal Linux LPE disclosed in two weeks, following Dirty Frag and Copy Fail (CVE-2026-31431, CISA KEV, May 15 patch deadline). Patches are rolling out for kernels released before May 13, 2026. Mitigation is identical to Dirty Frag: rmmod esp4 esp6 rxrpc (breaks IPsec VPNs and AFS). Organizations running non-containerized Linux exposed via SSH or web shells should patch immediately.

  2. update from access.redhat.com

    CVE-2026-46300 - Red Hat Customer Portal advisory

    access.redhat.com · 154d ago · May 13th, 2026

    Red Hat's CVE advisory (dated 13 May 2026) rates CVE-2026-46300 Important with CVSS 3.1 score 7.8 (AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H). It confirms the flaw allows a low-privileged local attacker to write arbitrary bytes into the page cache of read-only files in the Linux XFRM ESP-in-TCP subsystem, leading to root privilege escalation without user interaction.

  3. update from openwall.net

    [PATCH net] skbuff: preserve shared-frag marker during coalescing (original disclosure by William Bowling)

    openwall.net · 154d ago · May 13th, 2026

    On 13 May 2026 researcher William Bowling (vakzz@zellic.io) posted the kernel patch that fixes the skb coalescing regression (SKBFL_SHARED_FRAG propagation failure) that creates the Fragnesia vulnerability. The email confirms the bug is a separate regression from Dirty Frag (CVE-2026-43284) in the XFRM ESP-in-TCP path and that exploitation allows in-place decryption over page-cache-backed frags.

  4. update from tenable.com

    Fragnesia CVE-2026-46300 — Third Linux Kernel LPE in Two Weeks, Patches Available

    tenable.com · 152d ago · May 15th, 2026

    A public PoC confirmed working on Ubuntu modifies /usr/bin/su in the page cache without changing the on-disk binary. Kernel patches were released May 13; AlmaLinux and Fedora are patched, while Ubuntu, Debian, RHEL, and openSUSE remain vulnerable. The module blacklist mitigation (rmmod esp4 esp6 rxrpc) that protects against Dirty Frag also protects against Fragnesia — organizations that applied only kernel patches without the blacklist are not protected.

  5. update from github.com

    Fragnesia (CVE-2026-46300) — Dirty Frag Regression Creates New Universal Linux LPE with Public PoC — All Kernels Before May 13 Affected

    github.com · 140d ago · May 27th, 2026

    The fix for Dirty Frag changed how skb_try_coalesce() propagates SKBFL_SHARED_FRAG, and that change accidentally dropped the flag along the espintcp ULP-transition path. The result: 192 bytes per trigger of AES-GCM keystream XOR directly into the page cache of any user-readable file — no race condition required. The on-disk binary is untouched (a reboot clears the modification). The exploit requires user+network namespace access (CAP_NET_ADMIN from unshare), making it slightly more constrained than Copy Fail — but effective on any distribution where kernel.apparmor_restrict_unprivileged_userns is not enforced. Workaround: rmmod esp4 esp6 and block via modprobe config. No CISA KEV status yet, but the public PoC and trivial exploitation surface make this an urgent patching priority.

Source on GitHub