Null Pointer Dereference
A null pointer dereference occurs when a program attempts to access memory through a pointer that has been set to NULL (address 0x0).
How It Works
A null pointer dereference occurs when a program attempts to access memory through a pointer that has been set to NULL (address 0x0). In normal operation, pointers should reference valid memory locations before use. When a pointer is NULL—either uninitialized, explicitly set to NULL, or returned as NULL from a failed allocation—and the program tries to read from, write to, or execute code at that address, the operating system intervenes. On modern systems, accessing address zero triggers a segmentation fault that immediately terminates the process.
Attackers exploit this by manipulating program logic to force null pointer conditions. Common techniques include triggering allocation failures in low-memory conditions, providing malformed input that bypasses initialization checks, or exploiting race conditions where a pointer is checked for NULL but becomes NULL before use. The attacker identifies code paths where null checks are missing or inadequate, then crafts inputs to reach those vulnerable states.
On legacy systems without memory protection, attackers could map their own code at address zero, converting a crash into arbitrary code execution. Modern operating systems prevent this through mmap_min_addr restrictions that prohibit mapping memory below a threshold (typically 64KB). This mitigation has largely relegated null pointer dereferences to denial-of-service attacks rather than remote code execution vectors.
Impact
- Service disruption: Immediate process crash, taking down the vulnerable application or daemon
- Availability attacks: Repeated crashes forcing system restarts or service downtime
- Limited code execution: On unpatched legacy systems (pre-2009 Linux kernels, older embedded devices) where address zero mapping is possible
- Privilege escalation: In kernel-mode drivers where null dereferences can be exploited to execute attacker code with system privileges
Real-World Examples
The Linux kernel suffered from CVE-2009-2908, where null pointer dereferences in various subsystems could be exploited on systems allowing mmap at address zero. Attackers could map malicious code at NULL and trigger kernel null dereferences to achieve privilege escalation. This prompted the introduction of mmap_min_addr protections.
Microsoft Windows drivers have been frequent targets, including CVE-2020-17087 in the Windows kernel cryptography driver. Attackers triggered null pointer dereferences in kernel mode, which on older Windows versions could be exploited for local privilege escalation by controlling the null page.
Web browsers have experienced denial-of-service through null dereferences when parsing malformed content. Firefox CVE-2019-11707 involved a null pointer dereference in the IonMonkey JIT compiler, allowing attackers to crash the browser with specially crafted JavaScript, though not achieve code execution due to modern protections.
Mitigation
- Explicit null checks: Validate all pointers before dereferencing, especially after allocation or function calls that may return NULL
- Static analysis tools: Deploy analyzers like Coverity, Clang Static Analyzer, or PVS-Studio to detect missing null checks during development
- Address space layout: Enable
mmap_min_addrkernel protection (standard on modern Linux, typically 65536 bytes) - Fuzzing: Use AFL, libFuzzer, or similar tools to stress-test error handling paths and allocation failures
- Safe coding practices: Initialize pointers to NULL, use smart pointers in C++, adopt languages with built-in null safety
- Runtime bounds checking: Enable AddressSanitizer during testing to catch null dereferences immediately
Recent CVEs (4367)
The IOAccelSharedUserClient2::page_off_resource method in Apple iOS before 9.3.2, OS X before 10.11.5, tvOS before 9.2.1, and watchOS before 2.2.1 allows attackers to execute arbitrary code in a. Rated high severity (CVSS 7.8), this vulnerability is no authentication required, low attack complexity. Public exploit code available and no vendor patch available.
ImageIO in Apple iOS before 9.3.2, OS X before 10.11.5, tvOS before 9.2.1, and watchOS before 2.2.1 allows remote attackers to cause a denial of service (NULL pointer dereference) via a crafted image. Rated medium severity (CVSS 6.5), this vulnerability is remotely exploitable, no authentication required, low attack complexity. No vendor patch available.
CoreCapture in Apple iOS before 9.3.2, OS X before 10.11.5, tvOS before 9.2.1, and watchOS before 2.2.1 allows attackers to execute arbitrary code in a privileged context or cause a denial of service. Rated high severity (CVSS 7.8), this vulnerability is no authentication required, low attack complexity. Public exploit code available and no vendor patch available.
The treo_attach function in drivers/usb/serial/visor.c in the Linux kernel before 4.5 allows physically proximate attackers to cause a denial of service (NULL pointer dereference and system crash) or. Rated medium severity (CVSS 4.6), this vulnerability is no authentication required, low attack complexity. Public exploit code available.
The aiptek_probe function in drivers/input/tablet/aiptek.c in the Linux kernel before 4.4 allows physically proximate attackers to cause a denial of service (NULL pointer dereference and system. Rated medium severity (CVSS 4.6), this vulnerability is no authentication required, low attack complexity. Public exploit code available.
The PCI backend driver in Xen, when running on an x86 system and using Linux 3.1.x through 4.3.x as the driver domain, allows local guest administrators to hit BUG conditions and cause a denial of. Rated medium severity (CVSS 6.0), this vulnerability is low attack complexity. No vendor patch available.
The resolver in nginx before 1.8.1 and 1.9.x before 1.9.10 allows remote attackers to cause a denial of service (invalid pointer dereference and worker process crash) via a crafted UDP DNS response. Rated high severity (CVSS 7.5), this vulnerability is remotely exploitable, no authentication required, low attack complexity. Epss exploitation probability 78.8%.
The nf_nat_redirect_ipv4 function in net/netfilter/nf_nat_redirect.c in the Linux kernel before 4.4 allows remote attackers to cause a denial of service (NULL pointer dereference and system crash) or. Rated critical severity (CVSS 9.8), this vulnerability is remotely exploitable, no authentication required, low attack complexity.
IOKit SCSI in Apple iOS before 9.2, OS X before 10.11.2, tvOS before 9.1, and watchOS before 2.1 allows attackers to execute arbitrary code in a privileged context or cause a denial of service (NULL. Rated high severity (CVSS 7.8), this vulnerability is no authentication required, low attack complexity. Public exploit code available and no vendor patch available.
crypto/rsa/rsa_ameth.c in OpenSSL 1.0.1 before 1.0.1q and 1.0.2 before 1.0.2e allows remote attackers to cause a denial of service (NULL pointer dereference and application crash) via an RSA PSS. Rated high severity (CVSS 7.5), this vulnerability is remotely exploitable, no authentication required, low attack complexity. Epss exploitation probability 51.9%.
Adobe Reader and Acrobat 10.x before 10.1.15 and 11.x before 11.0.12, Acrobat and Acrobat Reader DC Classic before 2015.006.30060, and Acrobat and Acrobat Reader DC Continuous before 2015.008.20082. Rated medium severity (CVSS 5.0), this vulnerability is remotely exploitable, low attack complexity. This NULL Pointer Dereference vulnerability could allow attackers to crash the application by dereferencing a null pointer.
Adobe Reader and Acrobat 10.x before 10.1.15 and 11.x before 11.0.12, Acrobat and Acrobat Reader DC Classic before 2015.006.30060, and Acrobat and Acrobat Reader DC Continuous before 2015.008.20082. Rated medium severity (CVSS 5.0), this vulnerability is remotely exploitable, low attack complexity. This NULL Pointer Dereference vulnerability could allow attackers to crash the application by dereferencing a null pointer.
The kernel-mode drivers in Microsoft Windows Server 2003 SP2 and R2 SP2, Windows Vista SP2, Windows Server 2008 SP2 and R2 SP1, Windows 7 SP1, Windows 8, Windows 8.1, Windows Server 2012 Gold and R2,. Rated high severity (CVSS 7.2), this vulnerability is low attack complexity. Public exploit code available and EPSS exploitation probability 10.9%.
racoon/gssapi.c in IPsec-Tools 0.8.2 allows remote attackers to cause a denial of service (NULL pointer dereference and IKE daemon crash) via a series of crafted UDP requests. Rated high severity (CVSS 7.8), this vulnerability is remotely exploitable, low attack complexity. Public exploit code available and no vendor patch available.
Embedthis Appweb before 4.6.6 and 5.x before 5.2.1 allows remote attackers to cause a denial of service (NULL pointer dereference) via a Range header with an empty value, as demonstrated by "Range:. Rated medium severity (CVSS 5.0), this vulnerability is remotely exploitable, low attack complexity. Public exploit code available.
The kernel-mode drivers in Microsoft Windows Server 2003 SP2, Windows Vista SP2, Windows Server 2008 SP2 and R2 SP1, Windows 7 SP1, Windows 8, Windows 8.1, Windows Server 2012 Gold and R2, and. Rated medium severity (CVSS 5.6), this vulnerability is low attack complexity. This NULL Pointer Dereference vulnerability could allow attackers to crash the application by dereferencing a null pointer.
win32k.sys in the kernel-mode drivers in Microsoft Windows Server 2003 SP2, Windows Vista SP2, Windows Server 2008 SP2 and R2 SP1, Windows 7 SP1, Windows 8, Windows 8.1, Windows Server 2012 Gold and. Rated medium severity (CVSS 6.9). Public exploit code available and EPSS exploitation probability 13.6%.
The _bdf_parse_glyphs function in bdf/bdflib.c in FreeType before 2.5.4 does not properly handle a missing ENDCHAR record, which allows remote attackers to cause a denial of service (NULL pointer. Rated high severity (CVSS 7.5), this vulnerability is remotely exploitable, low attack complexity. Public exploit code available.
The krb5_ldap_get_password_policy_from_dn function in plugins/kdb/ldap/libkdb_ldap/ldap_pwd_policy.c in MIT Kerberos 5 (aka krb5) before 1.13.1, when the KDC uses LDAP, allows remote authenticated. Rated low severity (CVSS 3.5), this vulnerability is remotely exploitable. This NULL Pointer Dereference vulnerability could allow attackers to crash the application by dereferencing a null pointer.
The xdr_status_vector function in Firebird before 2.1.7 and 2.5.x before 2.5.3 SU1 allows remote attackers to cause a denial of service (NULL pointer dereference, segmentation fault, and crash) via. Rated medium severity (CVSS 5.0), this vulnerability is remotely exploitable, low attack complexity. Public exploit code available and no vendor patch available.
kernel/trace/trace_syscalls.c in the Linux kernel through 3.17.2 does not properly handle private syscall numbers during use of the ftrace subsystem, which allows local users to gain privileges or. Rated high severity (CVSS 7.8), this vulnerability is low attack complexity. Public exploit code available.
The sosendto function in slirp/udp.c in QEMU before 2.1.2 allows local users to cause a denial of service (NULL pointer dereference) by sending a udp packet with a value of 0 in the source port and. Rated low severity (CVSS 2.1), this vulnerability is low attack complexity.
The cache_merge_headers_out function in modules/cache/cache_util.c in the mod_cache module in the Apache HTTP Server before 2.4.11 allows remote attackers to cause a denial of service (NULL pointer. Rated medium severity (CVSS 5.0), this vulnerability is remotely exploitable, low attack complexity. This NULL Pointer Dereference vulnerability could allow attackers to crash the application by dereferencing a null pointer.
The acc_ctx_cont function in the SPNEGO acceptor in lib/gssapi/spnego/spnego_mech.c in MIT Kerberos 5 (aka krb5) 1.5.x through 1.12.x before 1.12.2 allows remote attackers to cause a denial of. Rated high severity (CVSS 7.8), this vulnerability is remotely exploitable, low attack complexity. This NULL Pointer Dereference vulnerability could allow attackers to crash the application by dereferencing a null pointer.
The sctp_assoc_update function in net/sctp/associola.c in the Linux kernel through 3.15.8, when SCTP authentication is enabled, allows remote attackers to cause a denial of service (NULL pointer. Rated high severity (CVSS 7.1), this vulnerability is remotely exploitable. Epss exploitation probability 12.8%.
The ssl3_send_client_key_exchange function in s3_clnt.c in OpenSSL before 0.9.8za, 1.0.0 before 1.0.0m, and 1.0.1 before 1.0.1h, when an anonymous ECDH cipher suite is used, allows remote attackers. Rated medium severity (CVSS 4.3), this vulnerability is remotely exploitable. Epss exploitation probability 91.4%.
The (1) asn1_read_value_type and (2) asn1_read_value functions in GNU Libtasn1 before 3.6 allows context-dependent attackers to cause a denial of service (NULL pointer dereference and crash) via a. Rated medium severity (CVSS 5.0), this vulnerability is remotely exploitable, low attack complexity.
The GIF decoder in QtGui in Qt before 5.3 allows remote attackers to cause a denial of service (NULL pointer dereference) via invalid width and height values in a GIF image. Rated medium severity (CVSS 4.3), this vulnerability is remotely exploitable. No vendor patch available.
The do_ssl3_write function in s3_pkt.c in OpenSSL 1.x through 1.0.1g, when SSL_MODE_RELEASE_BUFFERS is enabled, does not properly manage a buffer pointer during certain recursive calls, which allows. Rated medium severity (CVSS 4.3), this vulnerability is remotely exploitable. Epss exploitation probability 33.0%.
The rds_iw_laddr_check function in net/rds/iw.c in the Linux kernel through 3.14 allows local users to cause a denial of service (NULL pointer dereference and system crash) or possibly have. Rated medium severity (CVSS 4.7).
The rds_ib_laddr_check function in net/rds/ib.c in the Linux kernel before 3.12.8 allows local users to cause a denial of service (NULL pointer dereference and system crash) or possibly have. Rated medium severity (CVSS 4.7). Public exploit code available.
The gdImageCreateFromXpm function in gdxpm.c in libgd, as used in PHP 5.4.26 and earlier, allows remote attackers to cause a denial of service (NULL pointer dereference and application crash) via a. Rated medium severity (CVSS 4.3), this vulnerability is remotely exploitable. Public exploit code available and EPSS exploitation probability 12.1%.
The sctp_sf_do_5_1D_ce function in net/sctp/sm_statefuns.c in the Linux kernel through 3.13.6 does not validate certain auth_enable and auth_capable fields before making an sctp_sf_authenticate call,. Rated high severity (CVSS 7.8), this vulnerability is remotely exploitable, low attack complexity. This NULL Pointer Dereference vulnerability could allow attackers to crash the application by dereferencing a null pointer.
Smart Software Solutions (3S) CoDeSys Runtime Toolkit before 2.4.7.44 allows remote attackers to cause a denial of service (NULL pointer dereference and application crash) via unspecified vectors. Rated high severity (CVSS 7.1), this vulnerability is remotely exploitable. No vendor patch available.
The png_do_expand_palette function in libpng before 1.6.8 allows remote attackers to cause a denial of service (NULL pointer dereference and application crash) via (1) a PLTE chunk of zero bytes or. Rated medium severity (CVSS 6.5), this vulnerability is remotely exploitable, no authentication required, low attack complexity. Public exploit code available.
The setup_server_realm function in main.c in the Key Distribution Center (KDC) in MIT Kerberos 5 (aka krb5) before 1.10.7, when multiple realms are configured, allows remote attackers to cause a. Rated medium severity (CVSS 4.3), this vulnerability is remotely exploitable. This NULL Pointer Dereference vulnerability could allow attackers to crash the application by dereferencing a null pointer.
The ModSecurity module before 2.7.4 for the Apache HTTP Server allows remote attackers to cause a denial of service (NULL pointer dereference, process crash, and disk consumption) via a POST request. Rated medium severity (CVSS 5.0), this vulnerability is remotely exploitable, low attack complexity. Public exploit code available.
net/ceph/auth_none.c in the Linux kernel through 3.10 allows remote attackers to cause a denial of service (NULL pointer dereference and system crash) or possibly have unspecified other impact via an. Rated high severity (CVSS 7.8), this vulnerability is remotely exploitable, low attack complexity. No vendor patch available.
The prep_reprocess_req function in do_tgs_req.c in the Key Distribution Center (KDC) in MIT Kerberos 5 (aka krb5) before 1.10.5 does not properly perform service-principal realm referral, which. Rated medium severity (CVSS 4.0), this vulnerability is remotely exploitable, low attack complexity. This NULL Pointer Dereference vulnerability could allow attackers to crash the application by dereferencing a null pointer.
The pkinit_check_kdc_pkid function in plugins/preauth/pkinit/pkinit_crypto_openssl.c in the PKINIT implementation in the Key Distribution Center (KDC) in MIT Kerberos 5 (aka krb5) before 1.10.4 and. Rated medium severity (CVSS 5.0), this vulnerability is remotely exploitable, low attack complexity. This NULL Pointer Dereference vulnerability could allow attackers to crash the application by dereferencing a null pointer.
The pkinit_server_return_padata function in plugins/preauth/pkinit/pkinit_srv.c in the PKINIT implementation in the Key Distribution Center (KDC) in MIT Kerberos 5 (aka krb5) before 1.10.4 attempts. Rated medium severity (CVSS 5.0), this vulnerability is remotely exploitable, low attack complexity. This NULL Pointer Dereference vulnerability could allow attackers to crash the application by dereferencing a null pointer.
fits-io.c in GIMP before 2.8.1 allows remote attackers to cause a denial of service (NULL pointer dereference and application crash) via a malformed XTENSION header of a .fit file, as demonstrated. Rated medium severity (CVSS 4.3), this vulnerability is remotely exploitable. Public exploit code available and no vendor patch available.
Adobe Flash Player before 10.3.183.20 and 11.x before 11.3.300.257 on Windows and Mac OS X; before 10.3.183.20 and 11.x before 11.2.202.236 on Linux; before 11.1.111.10 on Android 2.x and 3.x; and. Rated critical severity (CVSS 9.3), this vulnerability is remotely exploitable. No vendor patch available.
The mem_cgroup_usage_unregister_event function in mm/memcontrol.c in the Linux kernel before 3.2.10 does not properly handle multiple events that are attached to the same eventfd, which allows local. Rated medium severity (CVSS 5.5), this vulnerability is low attack complexity. Public exploit code available.
The regset (aka register set) feature in the Linux kernel before 3.2.10 does not properly handle the absence of .get and .set methods, which allows local users to cause a denial of service (NULL. Rated high severity (CVSS 7.8), this vulnerability is low attack complexity. This NULL Pointer Dereference vulnerability could allow attackers to crash the application by dereferencing a null pointer.
Alpine Linux: dotnet8-runtime fixed in 8.0.2-r0
Capstone disassembly framework package in Alpine Linux has been patched at version 5.0.8-r0, addressing an unspecified vulnerability. The nature of the flaw, affected attack surface, and potential impact are not disclosed in available intelligence - only the vendor-reported fix version is confirmed. Security teams using Alpine Linux with the capstone package should treat this as a package-level security update requiring upgrade, pending further vendor disclosure.