High [CVE-2023-4911] buffer overflow in ld.so leading to privilege escalation
This high-severity Red Hat Linux advisory covers CVE-2023-4911 affecting Red Hat Enterprise Linux 8.6 Extended Update Support, Red Hat Enterprise Linux 9.0 Extended Update Support, Red Hat Virtualization 4 for Red Hat Enterprise Linux 8.
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Summary
A buffer overflow was discovered in the GNU C Library's dynamic loader ld.so while processing the GLIBC_TUNABLES environment variable. This issue could allow a local attacker to use maliciously crafted GLIBC_TUNABLES environment variables when launching binaries with SUID permission to execute code with elevated privileges.
This vulnerability was introduced in glibc version 2.34. RHEL-8 ships glibc 2.28, which is not originally affected by this vulnerability.
RHEL-8.4 and older are not affected by this vulnerability. Red Hat severity: Important — CVSS 7.8 (CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H).
Weakness: CWE-122. Affected Red Hat products: Red Hat Enterprise Linux 8; Red Hat Enterprise Linux 8.6 Extended Update Support; Red Hat Enterprise Linux 9; Red Hat Enterprise Linux 9.0 Extended Update Support; Red Hat Virtualization 4 for Red Hat Enterprise Linux 8.
Red Hat lists Red Hat Enterprise Linux 6; Red Hat Enterprise Linux 7 as not affected. Red Hat fixing advisory: RHSA-2023:5455, RHSA-2023:5476, RHSA-2023:5453, RHSA-2023:5454, RHSA-2024:0033.
Affected products named by the advisory: Red Hat package: glibc.
CISA Known Exploited Vulnerability
- Listed:
- Nov 21, 2023 · federal remediation due Dec 12, 2023
- Required action:
- Apply mitigations per vendor instructions or discontinue use of the product if mitigations are unavailable.
- Ransomware use:
- Unknown
KEV is a prioritization signal from CISA — remediation detail still comes from the vendor advisory.
Affected versions
No affected-version range was extracted from the source record. The vendor advisory is authoritative — check it before change work.
Official advisory · high-confidence parse· fetched 5 days ago·verify at source
- glibc-0:2.28-225.el8_8.6
- glibc-0:2.28-189.6.el8_6
- glibc-0:2.34-60.el9_2.7
- glibc-0:2.34-28.el9_0.4
- redhat-release-virtualization-host-0:4.5.3-10.el8ev
- redhat-virtualization-host-0:4.5.3-202312060823_8.6
- RHSA-2023:5455
- RHSA-2023:5476
- RHSA-2023:5453
- RHSA-2023:5454
- RHSA-2024:0033
Official advisory · high-confidence parse· fetched 5 days ago·verify at source
Mitigation checklist
- For customers who cannot update immediately and do not have Secure Boot feature enabled, the issue can be mitigated using the provided SystemTap script with the following steps. When enabled, any setuid program invoked with GLIBC_TUNABLES in the environment will be terminated immediately. To invoke the setuid program, users will then have to unset or clear the GLIBC_TUNABLES envvar, e.g. `GLIBC_TUNABLES= sudo` . Note that these mitigation steps will need to be repeated if the system is rebooted. 1) Install required systemtap packages and dependencies as per - https://access.redhat.com/solutions/5441 2) Create the following systemtap script, and name it stap_block_suid_tunables.stp: ~~~ function has_tunable_string:long() { name = "GLIBC_TUNABLES" mm = @task(task_current())->mm; if (mm) { env_start = @mm(mm)->env_start; env_end = @mm(mm)->env_end; if (env_start != 0 && env_end != 0) while (env_end > env_start) { cur = user_string(env_start, ""); env_name = tokenize(cur, "="); if (env_name == name && tokenize("", "") != "") return 1; env_start += strlen (cur) + 1 } } return 0; } probe process("/lib*/ld*.so*").function("__tunables_init") { atsecure = 0; /* Skip processing if we can't read __libc_enable_secure, e.g. core dump handler (systemd-cgroups-agent and systemd-coredump). */ try { atsecure = @var("__libc_enable_secure"); } catch { printk (4, sprintf ("CVE-2023-4911: Skipped check: %s (%d)", execname(), pid())); } if (atsecure && has_tunable_string ()) raise (9); } ~~~ 3) Load the systemtap module into the running kernel: ~~~ stap -g -F -m stap_block_suid_tunables stap_block_suid_tunables.stp ~~~ 4) Ensure the module is loaded: ~~~ lsmod | grep -i stap_block_suid_tunables stap_block_suid_tunables 249856 0 ~~~ 5) Once the glibc package is updated to the version containing the fix, the systemtap generated kernel module can be removed by running: ~~~ rmmod stap_block_suid_tunables ~~~ If Secure Boot is enabled on a system, the SystemTap module must be signed. An external compiling server can be used to sign the generated kernel module with a key enrolled into the kernel's keyring or starting with SystemTap 4.7 you can sign a module without a compile server. See further information here - https://www.redhat.com/sysadmin/secure-boot-systemtap
Official advisory · high-confidence parse· fetched 5 days ago·verify at source
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