VulnerabilityPublished 27 Jan 2021Updated 9 Jun 2025

CVE-2021-3326: GNU C Library · Reachable Assertion

Source CVE Database V5

Not known to be exploited · CVSS 7.5 High.

Data as of 26 Oct 2026, 14:05 UTC

CVSS 3.1 base score

7.5High

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

EPSS: 3.8% chance of exploitation in 30 days – higher than 90% 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:N/I:N/A:H

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

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: None: There is no loss of confidentiality within the impacted component.
Integrity: None: There is no loss of integrity within the impacted component.
Availability: High: There is total loss of availability, resulting in the attacker being able to fully deny access to resources in the impacted component; this loss is either sustained (while the attacker continues to deliver the attack) or persistent (the condition persists even after the attack has completed). Alternatively, the attacker has the ability to deny some availability, but the loss of availability presents a direct, serious consequence to the impacted component (e.g., the attacker cannot disrupt existing connections, but can prevent new connections; the attacker can repeatedly exploit a vulnerability that, in each instance of a successful attack, leaks a only small amount of memory, but after repeated exploitation causes a service to become completely unavailable).

Definitions: FIRST CVSS v3.1 specification.

Exploitation evidence

Disclosed: evidence found.
CVE published 27 Jan 2021
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 26 Oct 2026.

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 or the CVSS exploit maturity 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

Affected software

Product	Affected	Fixed in
Debiandebian/libc6`pkg:deb/debian/libc6`Other threats	Affected <=2.32	Fixed in–

Check your own hosts for these packages with threat-finder (opens in a new tab), our free open-source scanner.

AI-suggested

To mitigate CVE-2021-3326, European organizations should prioritize updating the GNU C Library to a patched version beyond 2.32 where this vulnerability is addressed. In the interim, organizations can implement input validation and sanitization to detect and reject malformed ISO-2022-JP-3 sequences before they reach the iconv function. Application-level logging and monitoring should be enhanced to detect abnormal crashes or assertion failures related to encoding conversions. Network-level protections such as Web Application Firewalls (WAFs) or Intrusion Prevention Systems (IPS) can be tuned to detect and block suspicious payloads containing malformed ISO-2022-JP-3 sequences. Additionally, organizations should conduct thorough testing of applications that rely on iconv to ensure they handle encoding errors gracefully and do not crash unexpectedly.

Description

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 encoding, fails an assertion in the code path and aborts the program, potentially resulting in a denial of service.

Impact

For European organizations, the impact of CVE-2021-3326 can be substantial, particularly for those running Linux-based infrastructure that processes text data in various encodings, including ISO-2022-JP-3. This encoding is primarily used for Japanese text, so organizations involved in international communications, software development, or data processing involving Japanese language content are at higher risk. A successful exploitation would cause critical services or applications to crash, leading to service outages and potential disruption of business operations. This can affect web servers, mail servers, or any backend systems that utilize glibc's iconv function for encoding conversions. The denial of service could be leveraged by attackers to degrade service availability or as part of a larger attack strategy. Given the widespread use of glibc in European data centers and cloud environments, the vulnerability poses a risk to availability and operational continuity, especially in sectors such as finance, telecommunications, and government services where uptime is critical.

CWE-617Reachable Assertion (opens in a new tab)
Base weakness
The product contains an assert() or similar statement that can be triggered by an attacker, which leads to an application exit or other behavior that is more severe than necessary.
Implementation
Make sensitive open/close operation non reachable by directly user-controlled data (e.g. open/close resources)
Implementation · Input Validation
Perform input validation on user data.
From MITRE CWE, MITRE CAPEC and OWASP (Top 10, OpenCRE).

References

Community reviews

Loading reviews…

Exploitation evidence

What to do

Affected software

Description

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

WeaknessesCWE-617

Technical details

References

Community reviews

Related threats