CVE-2021-3998VulnerabilityPublished 24 Aug 2022Updated 9 Jun 2025

CVE-2021-3998: glibc · - Out-of-bounds Read

Affects glibcSource CVE Database V5

Not known to be exploited · CVSS 7.5 High.

Data as of 25 Oct 2026, 19:02 UTC

CVSS 3.1 base score

7.5High

How severe the flaw is on the 0–10 CVSS scale.

EPSS: 2.2% chance of exploitation in 30 days – higher than 82% of CVEsExploit Prediction Scoring System: the likelihood attackers will use this flaw soon.

CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:N/A:N

Attack Vector: Network
Attack Complexity: Low
Privileges Required: None
User Interaction: None
Scope: Unchanged
Confidentiality: High
Integrity: None
Availability: None

Bold values are the worst case: easiest to exploit or largest impact.

Attack Vector: Network: The vulnerable component is bound to the network stack and the set of possible attackers extends beyond the other options listed, up to and including the entire Internet. Such a vulnerability is often termed 'remotely exploitable' and can be thought of as an attack being exploitable at the protocol level one or more network hops away (e.g., across one or more routers).
Attack Complexity: Low: Specialized access conditions or extenuating circumstances do not exist. An attacker can expect repeatable success against the vulnerable component.
Privileges Required: None: The attacker is unauthorized prior to attack, and therefore does not require any access to settings or files to carry out an attack.
User Interaction: None: The vulnerable system can be exploited without any interaction from any user.
Scope: Unchanged: An exploited vulnerability can only affect resources managed by the same security authority. In this case, the vulnerable component and the impacted component are either the same, or both are managed by the same security authority.
Confidentiality: High: There is total loss of confidentiality, resulting in all resources within the impacted component being divulged to the attacker. Alternatively, access to only some restricted information is obtained, but the disclosed information presents a direct, serious impact.
Integrity: None: There is no loss of integrity within the impacted component.
Availability: None: There is no impact to availability within the impacted component.

Definitions: FIRST CVSS v3.1 specification.

Exploitation evidence

Disclosed: evidence found.
CVE published 24 Aug 2022
Detectable: no evidence on record.
No public nuclei template indexed
Weaponised: no evidence on record.
No public exploit code indexed in Metasploit or Exploit-DB
Exploited in the wildExploited: no evidence on record.
Not in CISA KEV and no source reports exploitation
Observed by OffSeq MirageSeen by Mirage: no evidence on record.
No attack traffic recorded by OffSeq Mirage sensors

A missing step is not evidence of safety. Sources: cve.org (opens in a new tab), the Metasploit, Exploit-DB and nuclei-templates index as of 2026-10-25.

Disclosed: The CVE record is public on cve.org. Its publication is t = 0.
Detectable: A public nuclei template can find exposed instances, for defenders and attackers alike.
Weaponised: Public exploit code exists in Metasploit or Exploit-DB, or CISA SSVC reports a public proof of concept.
Exploited in the wild: CISA KEV lists it, CISA SSVC rates exploitation active, or a source reports attacks.
Observed by OffSeq Mirage: OffSeq Mirage honeypot sensors recorded attack traffic for this CVE, or found exposed hosts without attack traffic.

Moments are spaced evenly, not to scale; a dashed line marks a gap of six months or more. Deltas count from t = 0. Sources that give only a date (CISA KEV, Exploit-DB, or a time of exactly 00:00Z) read “same day” rather than hours. Metasploit modules carry the flaw’s disclosure date, not their release date, and nuclei templates carry no date, so both appear above but not on the timeline.

What to do

AI-suggested

To mitigate CVE-2021-3998 effectively, European organizations should prioritize the following actions: 1) Immediate patching: Upgrade glibc to a version where this vulnerability is fixed (check distributions for updated packages, e.g., glibc 2.34 or later). 2) Audit and monitor: Identify all systems running affected glibc versions, including containers and embedded devices, and monitor logs for suspicious usage of realpath() or unusual file path resolution activities. 3) Restrict input vectors: Harden applications and services that accept file path inputs by validating and sanitizing inputs rigorously to reduce the attack surface. 4) Implement memory protection mechanisms: Use security features such as Address Space Layout Randomization (ASLR) and stack canaries to complicate exploitation attempts. 5) Network segmentation: Limit exposure of vulnerable systems by segmenting networks and restricting access to critical servers. 6) Incident response readiness: Prepare detection and response plans for potential exploitation attempts, including anomaly detection for unexpected memory disclosures. 7) Vendor coordination: Engage with Linux distribution vendors and software suppliers to ensure timely updates and patches are applied across all environments.

Description

A flaw was found in glibc. The realpath() function can mistakenly return an unexpected value, potentially leading to information leakage and disclosure of sensitive data.

Impact

For European organizations, the impact of CVE-2021-3998 can be substantial given the widespread use of glibc in Linux environments across government, finance, healthcare, telecommunications, and critical infrastructure sectors. Information leakage could lead to exposure of sensitive personal data protected under GDPR, intellectual property, or security credentials, increasing the risk of further attacks such as privilege escalation or lateral movement within networks. Organizations running vulnerable versions of glibc on their servers or endpoints may inadvertently expose confidential information to attackers capable of manipulating file path inputs. This is particularly concerning for cloud service providers and data centers in Europe that host multi-tenant environments where isolation between tenants is critical. The vulnerability's ease of exploitation without authentication or user interaction further elevates the risk profile, making it a viable vector for automated scanning and exploitation attempts. Although no active exploits are currently known, the potential for future weaponization necessitates proactive mitigation to protect sensitive European digital assets and comply with stringent data protection regulations.

CWE-125Out-of-bounds Read (opens in a new tab)
Base weaknessCWE Top 25 (2025): #8
The product reads data past the end, or before the beginning, of the intended buffer.
Implementation · Input Validation
Assume all input is malicious. Use an "accept known good" input validation strategy, i.e., use a list of acceptable inputs that strictly conform to specifications. Reject any input that does not strictly conform to specifications, or transform it into something that does.
Architecture and Design · Language Selection
Use a language that provides appropriate memory abstractions.
OWASP Cheat Sheets
XML Security (opens in a new tab)
Mass Assignment (opens in a new tab)
OWASP ASVS 4.0.3
V13.3.1 (opens in a new tab)
V5.1.4 (opens in a new tab)
V5.1.3 (opens in a new tab)
Attack patterns
Overread Buffers (opens in a new tab)
From MITRE CWE, MITRE CAPEC and OWASP (Top 10, OpenCRE).

References

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Exploitation evidence

What to do

Description

AI analysisMachine-generated, updated 10 Jul 2025, 20:19 UTC

WeaknessesCWE-125

Technical details

References

Community reviews

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