Linux Kernel MPI Integer Underflow DoS
CVE-2026-43492 Published on May 19, 2026
lib/crypto: mpi: Fix integer underflow in mpi_read_raw_from_sgl()
In the Linux kernel, the following vulnerability has been resolved:
lib/crypto: mpi: Fix integer underflow in mpi_read_raw_from_sgl()
Yiming reports an integer underflow in mpi_read_raw_from_sgl() when
subtracting "lzeros" from the unsigned "nbytes".
For this to happen, the scatterlist "sgl" needs to occupy more bytes
than the "nbytes" parameter and the first "nbytes + 1" bytes of the
scatterlist must be zero. Under these conditions, the while loop
iterating over the scatterlist will count more zeroes than "nbytes",
subtract the number of zeroes from "nbytes" and cause the underflow.
When commit 2d4d1eea540b ("lib/mpi: Add mpi sgl helpers") originally
introduced the bug, it couldn't be triggered because all callers of
mpi_read_raw_from_sgl() passed a scatterlist whose length was equal to
"nbytes".
However since commit 63ba4d67594a ("KEYS: asymmetric: Use new crypto
interface without scatterlists"), the underflow can now actually be
triggered. When invoking a KEYCTL_PKEY_ENCRYPT system call with a
larger "out_len" than "in_len" and filling the "in" buffer with zeroes,
crypto_akcipher_sync_prep() will create an all-zero scatterlist used for
both the "src" and "dst" member of struct akcipher_request and thereby
fulfil the conditions to trigger the bug:
sys_keyctl()
keyctl_pkey_e_d_s()
asymmetric_key_eds_op()
software_key_eds_op()
crypto_akcipher_sync_encrypt()
crypto_akcipher_sync_prep()
crypto_akcipher_encrypt()
rsa_enc()
mpi_read_raw_from_sgl()
To the user this will be visible as a DoS as the kernel spins forever,
causing soft lockup splats as a side effect.
Fix it.
Products Associated with CVE-2026-43492
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Affected Versions
Linux:- Version 2d4d1eea540b27c72488fd1914674c42473d53df and below 2aa77a18dc7f2670497fe3ee5acbeda0b57659e5 is affected.
- Version 2d4d1eea540b27c72488fd1914674c42473d53df and below 26d3a97ad46c7a9226ec04d4bf35bd4998a97d16 is affected.
- Version 2d4d1eea540b27c72488fd1914674c42473d53df and below 8637dfb4c1d8a7026ef681f2477c6de8b71c4003 is affected.
- Version 2d4d1eea540b27c72488fd1914674c42473d53df and below 30e513e755bb381afce6fb57cdc8694136193f22 is affected.
- Version 2d4d1eea540b27c72488fd1914674c42473d53df and below 8c2f1288250a90a4b5cabed5d888d7e3aeed4035 is affected.
- Version 4.4 is affected.
- Before 4.4 is unaffected.
- Version 6.6.140, <= 6.6.* is unaffected.
- Version 6.12.88, <= 6.12.* is unaffected.
- Version 6.18.30, <= 6.18.* is unaffected.
- Version 7.0.7, <= 7.0.* is unaffected.
- Version 7.1-rc1, <= * is unaffected.