CVE-2021-27645: The nameserver caching daemon (nscd) in the GNU C Library (aka glibc or libc6) 2.29 through 2.33, when processing a request for netgroup loo
Noroxi assessment
Priority: Monitor (action score 10/100)
- The sources we track (CISA KEV, Exploit-DB, Metasploit, Nuclei, GitHub) show no public exploit code or exploitation in the wild.
- Probability of exploitation in the next 30 days: 0.38% (FIRST EPSS).
- Someone with local access to the system can trigger it. A low-privileged account is enough. No user action is required. Special conditions such as timing or configuration are required.
- Fixed version: compat-libpthread-nonshared (AlmaLinux:8) 2.28-164.el8; glibc-benchtests (AlmaLinux:8) 2.28-164.el8; glibc-nss-devel (AlmaLinux:8) 2.28-164.el8.
- Mentioned 5 times in Turkish national cyber security advisories (siberguvenlik.gov.tr).
Low priority for now. Upgrade to compat-libpthread-nonshared (AlmaLinux:8) 2.28-164.el8; glibc-benchtests (AlmaLinux:8) 2.28-164.el8; glibc-nss-devel (AlmaLinux:8) 2.28-164.el8 or later.
Generated automatically from the record's data: CVSS (NVD and CNA), CISA KEV and SSVC, FIRST EPSS, exploit sources, fixed versions. How we calculate it
Primary sources: NVD · CVE.org · FIRST EPSS
The nameserver caching daemon (nscd) in the GNU C Library (aka glibc or libc6) 2.29 through 2.33, when processing a request for netgroup lookup, may crash due to a double-free, potentially resulting in degraded service or Denial of Service on the local system. This is related to netgroupcache.c.
- Published
- Feb 24, 2021
- Updated
- Oct 14, 2026
- EPSS
- 0.3% · 32th percentile
- CWE
- CWE-415
Report tools
Action score
10
Monitor
Low priority for now.
- CVSS
- 10 / 40 · 2.5 / 10
- CISA KEV
- 0 / 30 · Not listed
- EPSS
- 0 / 30 · 0.3%
CISA SSVC decision
- Exploitation
- none
- Automatable
- no
- Technical impact
- partial
Vulnrichment: CISA's decision-tree inputs.
CNA vs NVD score
- NVD
- 2.5
- CNA · mitre
- 2.5
- agree
The score given by the assigning authority versus NVD’s independent score. A gap means the severity is contested.
Get told when this record changes
- Not in KEV: no record of exploitation in the wild
- No public exploit code on record
- A fix has been released
If any of these changes, we'll tell you in the daily email digest.
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Noroxi analysis
What does it mean in your environment?
The assessment above is generated automatically from the record's data; it doesn't know your environment. Our team verifies on your systems whether this vulnerability is actually exploitable and which mitigation is enough.
We use this product, ask for helpAffected systems
Is your version affected?
Pick the product and type the version you run. It's compared with this record's version ranges in your browser; the version isn't sent anywhere.
| Vendor | Product | CPE |
|---|---|---|
| gnu | glibc | cpe:2.3:a:gnu:glibc |
| fedoraproject | fedora | cpe:2.3:o:fedoraproject:fedora |
| debian | debian linux | cpe:2.3:o:debian:debian_linux |
Affected versions
NVD version ranges (for catalog products). Add the product to your stack with a version and matching uses these.
- debian debian linux10.0
- fedoraproject fedora33
- fedoraproject fedora34
- gnu glibc2.29 and later · up to 2.33 inclusive
Package-level exposure
OSV and GitHub Advisory data: ecosystem, package and range. SBOM matching uses this table.
| Ecosystem | Package | Affected range | Fix |
|---|---|---|---|
| AlmaLinux:8 | compat-libpthread-nonshared | before 2.28-164.el8 | 2.28-164.el8 |
| AlmaLinux:8 | glibc-benchtests | before 2.28-164.el8 | 2.28-164.el8 |
| AlmaLinux:8 | glibc-nss-devel | before 2.28-164.el8 | 2.28-164.el8 |
| AlmaLinux:8 | glibc-static | before 2.28-164.el8 | 2.28-164.el8 |
| AlmaLinux:8 | glibc-utils | before 2.28-164.el8 | 2.28-164.el8 |
| AlmaLinux:8 | nss_hesiod | before 2.28-164.el8 | 2.28-164.el8 |
| Debian:10 | glibc | before 2.28-10+deb10u2 | 2.28-10+deb10u2 |
| Debian:12 | glibc | before 2.31-10 | 2.31-10 |
| Red Hat:enterprise_linux:8::appstream | compat-libpthread-nonshared | before 0:2.28-164.el8 | 0:2.28-164.el8 |
| Red Hat:enterprise_linux:8::appstream | glibc-debuginfo | before 0:2.28-164.el8 | 0:2.28-164.el8 |
| Red Hat:enterprise_linux:8::appstream | glibc-debuginfo-common | before 0:2.28-164.el8 | 0:2.28-164.el8 |
| Red Hat:enterprise_linux:8::appstream | glibc-utils | before 0:2.28-164.el8 | 0:2.28-164.el8 |
| Red Hat:enterprise_linux:8::baseos | glibc | before 0:2.28-164.el8 | 0:2.28-164.el8 |
| Red Hat:enterprise_linux:8::baseos | glibc-all-langpacks | before 0:2.28-164.el8 | 0:2.28-164.el8 |
| Red Hat:enterprise_linux:8::baseos | glibc-common | before 0:2.28-164.el8 | 0:2.28-164.el8 |
| Red Hat:enterprise_linux:8::baseos | glibc-devel | before 0:2.28-164.el8 | 0:2.28-164.el8 |
| Red Hat:enterprise_linux:8::baseos | glibc-headers | before 0:2.28-164.el8 | 0:2.28-164.el8 |
| Red Hat:enterprise_linux:8::baseos | glibc-langpack-aa | before 0:2.28-164.el8 | 0:2.28-164.el8 |
| Red Hat:enterprise_linux:8::baseos | glibc-langpack-af | before 0:2.28-164.el8 | 0:2.28-164.el8 |
| Red Hat:enterprise_linux:8::baseos | glibc-langpack-agr | before 0:2.28-164.el8 | 0:2.28-164.el8 |
| Red Hat:enterprise_linux:8::baseos | glibc-langpack-ak | before 0:2.28-164.el8 | 0:2.28-164.el8 |
| Red Hat:enterprise_linux:8::baseos | glibc-langpack-am | before 0:2.28-164.el8 | 0:2.28-164.el8 |
| Red Hat:enterprise_linux:8::baseos | glibc-langpack-an | before 0:2.28-164.el8 | 0:2.28-164.el8 |
| Red Hat:enterprise_linux:8::baseos | glibc-langpack-anp | before 0:2.28-164.el8 | 0:2.28-164.el8 |
+96
Same product
gnu: all recordsOther highest-scoring records for the same primary product.
- CVE-2023-4911Glibc: buffer overflow in ld.so leading to privilege escalationKEV80Now
- CVE-2015-0235Heap-based buffer overflow in the __nss_hostname_digits_dots function in glibc 2.2, and other 2.x versions before 2.18, allows context-depen68This week
- CVE-2015-7547Multiple stack-based buffer overflows in the (1) send_dg and (2) send_vc functions in the libresolv library in the GNU C Library (aka glibc 60This week
Published before and after this one in the same product
- ← EarlierCVE-2019-25013Jan 4, 2021 · The iconv feature in the GNU C Library (aka glibc or libc6) through 2.32, when processing invalid multi-byte input sequences in the EUC-KR e24Monitor
- ← EarlierCVE-2021-3326Jan 27, 2021 · The iconv function in the GNU C Library (aka glibc or libc6) 2.32 and earlier, when processing invalid input sequences in the ISO-2022-JP-3 31Monitor
- Later →CVE-2020-27618Feb 26, 2021 · The iconv function in the GNU C Library (aka glibc or libc6) 2.32 and earlier, when processing invalid multi-byte input sequences in IBM136422Monitor
Remediation
Which version to upgrade to
Fix versions compiled from the vendor, package registries and Microsoft. Verify the vendor's note before upgrading.
| Product / package | Fixed version | Source |
|---|---|---|
| almalinux:compat-libpthread-nonshared | 2.28-164.el8 · AlmaLinux:8 | Package registry (OSV) |
| almalinux:glibc-benchtests | 2.28-164.el8 · AlmaLinux:8 | Package registry (OSV) |
| almalinux:glibc-nss-devel | 2.28-164.el8 · AlmaLinux:8 | Package registry (OSV) |
| almalinux:glibc-static | 2.28-164.el8 · AlmaLinux:8 | Package registry (OSV) |
| almalinux:glibc-utils | 2.28-164.el8 · AlmaLinux:8 | Package registry (OSV) |
| almalinux:nss_hesiod | 2.28-164.el8 · AlmaLinux:8 | Package registry (OSV) |
| debian:glibc | 2.31-10 · Debian:12 | Package registry (OSV) |
| red hat:compat-libpthread-nonshared | 0:2.28-164.el8 · Red Hat:enterprise_linux:8::appstream | Package registry (OSV) |
| red hat:glibc | 0:2.28-164.el8 · Red Hat:enterprise_linux:8::baseos | Package registry (OSV) |
| red hat:glibc-all-langpacks | 0:2.28-164.el8 · Red Hat:enterprise_linux:8::baseos | Package registry (OSV) |
| red hat:glibc-common | 0:2.28-164.el8 · Red Hat:enterprise_linux:8::baseos | Package registry (OSV) |
| red hat:glibc-debuginfo | 0:2.28-164.el8 · Red Hat:enterprise_linux:8::appstream | Package registry (OSV) |
| red hat:glibc-debuginfo-common | 0:2.28-164.el8 · Red Hat:enterprise_linux:8::appstream | Package registry (OSV) |
| red hat:glibc-devel | 0:2.28-164.el8 · Red Hat:enterprise_linux:8::baseos | Package registry (OSV) |
| red hat:glibc-headers | 0:2.28-164.el8 · Red Hat:enterprise_linux:8::baseos | Package registry (OSV) |
| red hat:glibc-langpack-aa | 0:2.28-164.el8 · Red Hat:enterprise_linux:8::baseos | Package registry (OSV) |
| red hat:glibc-langpack-af | 0:2.28-164.el8 · Red Hat:enterprise_linux:8::baseos | Package registry (OSV) |
| red hat:glibc-langpack-agr | 0:2.28-164.el8 · Red Hat:enterprise_linux:8::baseos | Package registry (OSV) |
| red hat:glibc-utils | 0:2.28-164.el8 · Red Hat:enterprise_linux:8::appstream | Package registry (OSV) |
| rocky linux:glibc | 0:2.28-164.el8 · Rocky Linux:8 | Package registry (OSV) |
Exploit status
No known public exploit
No public exploit has been observed yet. That doesn't mean you're safe, only that the bar is a little higher.
Research context
For pentesters and researchers: attack profile, score disagreement, timeline, patch commits, credits, variant and chain candidates, bug bounty scope. All derived from existing data; no exploit code.
Timeline
From publication to today: proof of concept, Metasploit module, CISA KEV and fix record. Dates are as reported by the sources.
No dated events beyond publication.
No history yet (it accumulates with the daily EPSS job).
Patch and commit links
Commit, PR and diff links among the references. A starting point for patch-diffing and variant hunting; fixes, not exploits.
No commit or PR link among the references.
Credits
All researchersFinders, reporters and analysts named in the CNA record. Click a name for that researcher’s other records.
No credits in the CNA record.
Variant candidates
Same product, same weakness class, within 18 months. If the patch missed the root cause, the sibling bug is here.
No nightly-computed relations.
Chain candidates
An authentication bypass and a privilege-requiring bug in the same product, published close together: combined they may become an unauthenticated path.
—
Bug bounty scope
No known public program.
Source: bounty-targets-data (public HackerOne, Bugcrowd, Intigriti, YesWeHack listings).
National notice (Türkiye Cybersecurity Directorate / USOM)
Official security notices citing this record; remediation advice is on the agency's page.
- TR-22-0222 · Mar 15, 2022(RedHat Güvenlik Güncellemesi)
- TR-22-0184 · Mar 1, 2022(IBM Güvenlik Bülteni)
- TR-22-0113 · Feb 4, 2022(RedHat Güvenlik Güncellemesi)
- TR-22-0097 · Jan 28, 2022(RedHat Güvenlik Güncellemesi)
- TR-21-0963 · Dec 2, 2021(RedHat Güvenlik Güncellemesi)
Technical details
Attack conditions
- Someone with local access to the system can trigger it.
- A low-privileged account is enough.
- No user action is required.
- Special conditions such as timing or configuration are required.
If successful
- Confidentiality
- none
- Integrity
- none
- Availability
- low · the service can be disrupted
- Attack vector
- Local
- Attack complexity
- High
- Privileges required
- Low
- User interaction
- None
- Scope
- Unchanged
- Confidentiality impact
- None
- Integrity impact
- None
- Availability impact
- Low
Weakness class (CWE)
CWE-415 · Double FreeCVSS vector
CVSS:3.1/AV:L/AC:H/PR:L/UI:N/S:U/C:N/I:N/A:L
nvd-primary
Attack context
MITRE CAPEC attack patterns and ATT&CK techniques for this weakness class (CWE). A starting point for detection rules and threat hunting.
MITRE has no CAPEC/ATT&CK mapping for this CWE.
Change log
- Fix✗ → ✓
For records you follow, these changes also arrive as notifications. →
References
Show all references (6 more)Show less
- lists.fedoraproject.org/archives/list/package-announce%40lists.fedoraproject.org/message/7LZNT6KTMCCWPWXEOGSHD3YLYZKUGMH5/
- lists.fedoraproject.org/archives/list/package-announce%40lists.fedoraproject.org/message/I7TS26LIZSOBLGJEZMJX4PXT5BQDE2WS/
- security.gentoo.org/glsa/202107-07
- sourceware.org/bugzilla/show_bug.cgi?id=27462
- cert-portal.siemens.com/productcert/html/ssa-398330.html
- cert-portal.siemens.com/productcert/html/ssa-831302.html
Vendor advisories and official records. Exploit/PoC links are deliberately left out.