CVE-2023-4911
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Description
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.
Statement
This vulnerability was introduced in glibc version 2.34. RHEL-8 ships glibc 2.28, which is not originally affected by this vulnerability. However, the commit that introduced this vulnerability was backported to RHEL-8.5, making this version and onward vulnerable. RHEL-8.4 and older are not affected by this vulnerability.
Mitigation
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
Additional information
- Bugzilla 2238352: glibc: buffer overflow in ld.so leading to privilege escalation
- CWE-122: Heap-based Buffer Overflow
- FAQ: Frequently asked questions about CVE-2023-4911
External references
Common Vulnerability Scoring System (CVSS) Score Details
Important note
CVSS scores for open source components depend on vendor-specific factors (e.g. version or build chain). Therefore, Red Hat's score and impact rating can be different from NVD and other vendors. Red Hat remains the authoritative CVE Naming Authority (CNA) source for its products and services (see Red Hat classifications).
Red Hat | NVD | |
---|---|---|
CVSS v3 Base Score | 7.8 | 7.8 |
Attack Vector | Local | Local |
Attack Complexity | Low | Low |
Privileges Required | Low | Low |
User Interaction | None | None |
Scope | Unchanged | Unchanged |
Confidentiality Impact | High | High |
Integrity Impact | High | High |
Availability Impact | High | High |
CVSS v3 Vector
Red Hat: CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H
NVD: CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H
Acknowledgements
Red Hat would like to thank Qualys Research Labs for reporting this issue.
Frequently Asked Questions
Why is Red Hat's CVSS v3 score or Impact different from other vendors?
For more information, see https://access.redhat.com/solutions/762393.
My product is listed as "Under investigation" or "Affected", when will Red Hat release a fix for this vulnerability?
- "Under investigation" doesn't necessarily mean that the product is affected by this vulnerability. It only means that our Analysis Team is still working on determining whether the product is affected and how it is affected.
- "Affected" means that our Analysis Team has determined that this product is affected by this vulnerability and might release a fix to address this in the near future.
What can I do if my product is listed as "Will not fix"?
Available options depend mostly on the Impact of the vulnerability and the current Life Cycle phase of your product. Overall, you have the following options:
- Upgrade to a supported product version that includes a fix for this vulnerability (recommended).
- Apply a mitigation (if one exists).
- Open a support case to request a prioritization of releasing a fix for this vulnerability.
What can I do if my product is listed as "Fix deferred"?
Available options depend mostly on the Impact of the vulnerability and the current Life Cycle phase of your product. Overall, you have the following options:
- Apply a mitigation (if one exists).
- Open a support case to request a prioritization of releasing a fix for this vulnerability.
- Red Hat Engineering focuses on addressing high-priority issues based on their complexity or limited lifecycle support. Therefore, lower-priority issues will not receive immediate fixes.
What is a mitigation?
I have a Red Hat product but it is not in the above list, is it affected?
Why is my security scanner reporting my product as vulnerable to this vulnerability even though my product version is fixed or not affected?
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