CVE-2026-32849: NetBSD Integer Overflow DoS Vulnerability

CVE-2026-32849 Overview

CVE-2026-32849 is a signed integer overflow vulnerability ([CWE-190]) in the NetBSD kernel. The flaw resides in the cryptodev_op() function within sys/opencrypto/cryptodev.c. The local variable iov_len is declared as a signed int but receives an assignment from the unsigned cop->dst_len field. When cop->dst_len exceeds INT_MAX, undefined behavior occurs. A local attacker with access to /dev/crypto and a compression session type can submit a crafted dst_len value to trigger a kernel panic. NetBSD addressed the issue in commit ec8451e.

Critical Impact
A local user with /dev/crypto access can crash the NetBSD kernel through a NULL pointer dereference caused by corrupted UIO pointer arithmetic when CONFIG_SVS is disabled.

Affected Products

NetBSD versions prior to commit ec8451efc1565516aba9e7047e1a1a1ce7953a2f
Systems exposing /dev/crypto to local users
Kernels built with CONFIG_SVS disabled (heightened impact path)

Discovery Timeline

2026-05-18 - CVE-2026-32849 published to NVD
2026-05-18 - Last updated in NVD database

Technical Details for CVE-2026-32849

Vulnerability Analysis

The vulnerability stems from a type mismatch between the user-controlled cop->dst_len field and the kernel's internal iov_len variable. The crypt_op structure carries dst_len as an unsigned value supplied by userland through an ioctl against /dev/crypto. Inside cryptodev_op(), this value is copied into a signed int. Values greater than INT_MAX wrap into negative numbers when stored. The kernel subsequently uses this corrupted length in UIO (user I/O) pointer arithmetic without revalidating the result. When CONFIG_SVS (Separated Virtual address Space) is disabled, the resulting computation dereferences a NULL or invalid pointer, panicking the kernel.

Root Cause

The root cause is improper integer type handling [CWE-190]. The signed int iov_len cannot represent values above 2,147,483,647, while cop->dst_len is unsigned and accepts larger values. Sign conversion produces a negative length that propagates through subsequent buffer math.

Attack Vector

Exploitation requires local access and permission to open /dev/crypto. The attacker establishes a session of a compression algorithm type, then issues a CIOCCRYPT ioctl with dst_len set above INT_MAX. The resulting kernel panic produces a denial of service. No remote vector exists and confidentiality and integrity are not impacted.

// Patch metadata from the NetBSD upstream fix (commit ec8451e)
-/*	$NetBSD: crypto.c,v 1.131 2022/06/26 22:52:30 riastradh Exp $ */
+/*	$NetBSD: crypto.c,v 1.132 2026/04/29 14:49:51 christos Exp $ */

Source: NetBSD commit ec8451e

// Header signature changes hardening length parameters to size_t
-int cryptodev_mop(struct fcrypt *, struct crypt_n_op *, int, struct lwp *);
+int cryptodev_mop(struct fcrypt *, struct crypt_n_op *, size_t, struct lwp *);
-int cryptodev_msession(struct fcrypt *, struct session_n_op *, int);
+int cryptodev_msession(struct fcrypt *, struct session_n_op *, size_t);

Source: NetBSD commit ec8451e. The fix replaces signed int length parameters with size_t across the cryptodev interface to eliminate the overflow class entirely.

Detection Methods for CVE-2026-32849

Indicators of Compromise

Unexpected kernel panics on NetBSD hosts referencing cryptodev_op or opencrypto in stack traces
Crash dumps showing NULL pointer dereference within UIO buffer handling routines
Local processes opening /dev/crypto followed by abrupt system reboot or hang

Detection Strategies

Audit which local users and services hold read/write permissions on /dev/crypto
Hunt for processes issuing CIOCGSESSION followed by CIOCCRYPT ioctls with abnormally large dst_len values
Correlate kernel panic events with preceding userland activity against the crypto device

Monitoring Recommendations

Forward kernel message buffers and savecore dumps to a centralized log store for post-incident review
Alert on repeated unexpected reboots of NetBSD hosts within short time windows
Track process execution that opens /dev/crypto from non-privileged accounts

How to Mitigate CVE-2026-32849

Immediate Actions Required

Update NetBSD source trees to a revision including commit ec8451efc1565516aba9e7047e1a1a1ce7953a2f and rebuild the kernel
Restrict /dev/crypto permissions so that only trusted accounts and services can open the device
Enable CONFIG_SVS where supported to reduce the impact of corrupted kernel pointer arithmetic

Patch Information

The upstream fix is available in the NetBSD source repository at commit ec8451efc1565516aba9e7047e1a1a1ce7953a2f. The patch updates sys/opencrypto/crypto.c and sys/opencrypto/cryptodev_internal.h, converting affected length parameters from signed int to size_t. Additional context is published in the VulnCheck advisory and the NASM technical write-up.

Workarounds

Tighten file mode on /dev/crypto (for example, chmod 600 /dev/crypto) until the patched kernel is deployed
Disable or unload the cryptodev pseudo-device on systems that do not require userland access to in-kernel crypto
Limit shell access on multi-user systems to reduce the local attacker population

bash

# Restrict access to the crypto pseudo-device while preparing a patched kernel
ls -l /dev/crypto
chown root:wheel /dev/crypto
chmod 600 /dev/crypto

# Verify running kernel revision after patching
uname -v | grep -i netbsd