CVE-2021-22945VulnerabilityPublished 23 Sep 2021Updated 9 Jun 2025

CVE-2021-22945: https://github.com/curl/curl · Double Free

Affects https://github.com/curl/curlSource CVE Database V5

Not known to be exploited · CVSS 9.1 Critical : upgrade to 7.78.0 or 7.73.0 as a priority.

Data as of 25 Oct 2026, 19:02 UTC

CVSS 3.1 base score

9.1Critical

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

EPSS: 6.6% chance of exploitation in 30 days – higher than 93% of CVEsExploit Prediction Scoring System: the likelihood attackers will use this flaw soon.
Patch: Available – fixed in 7.78.0, 7.73.0

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

Attack Vector: Network
Attack Complexity: Low
Privileges Required: None
User Interaction: None
Scope: Unchanged
Confidentiality: High
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: 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: 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 23 Sep 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 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

Upgrade curl/curl to 7.78.0 or 7.73.0.

Affected software

Product	Affected	Fixed in
GitHubcurl/curl`pkg:github/curl/curl`Other threats	Affected <7.73.0 <7.78.0	Fixed in 7.73.0 7.78.0

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

AI-suggested

European organizations should take the following specific actions to mitigate CVE-2021-22945: 1) Inventory all software and devices that use libcurl, focusing on versions 7.73.0 through 7.78.0, especially those handling MQTT communications. 2) Upgrade libcurl to the latest stable version beyond 7.78.0 where the vulnerability is patched. 3) For embedded or third-party products that incorporate libcurl, coordinate with vendors to obtain patched versions or apply vendor-provided mitigations. 4) Implement network-level controls to monitor and restrict MQTT traffic to trusted sources, reducing exposure to malicious MQTT servers or crafted payloads. 5) Employ runtime protections such as memory corruption mitigations (e.g., ASLR, DEP) to reduce exploitation success. 6) Conduct targeted penetration testing and fuzzing on MQTT communication components to identify residual vulnerabilities. 7) Maintain robust incident detection capabilities to identify unusual crashes or memory corruption events that may indicate exploitation attempts. These steps go beyond generic patching advice by emphasizing supply chain awareness, network segmentation, and proactive detection tailored to MQTT and libcurl usage contexts.

Description

When sending data to an MQTT server, libcurl <= 7.73.0 and 7.78.0 could in some circumstances erroneously keep a pointer to an already freed memory area and both use that again in a subsequent call to send data and also free it *again*.

Impact

For European organizations, the impact of CVE-2021-22945 can be substantial, especially for those utilizing MQTT-based messaging in IoT deployments, industrial control systems, or cloud services that incorporate libcurl for data transfer. Exploitation could lead to denial of service through application crashes or potentially allow attackers to execute arbitrary code, compromising confidentiality and availability of critical systems. This is particularly concerning for sectors such as manufacturing, energy, healthcare, and telecommunications, where MQTT is commonly used for device telemetry and control. Disruption or compromise of these systems could result in operational downtime, data breaches, or safety risks. Additionally, since libcurl is embedded in many software products, the vulnerability could propagate through supply chains, affecting a broad range of applications and services across Europe. The critical CVSS score underscores the urgency for organizations to assess their exposure and remediate promptly to prevent exploitation.

CWE-415Double Free (opens in a new tab)
Variant weaknessLikelihood of exploit: High
The product calls free() twice on the same memory address.
Architecture and Design
Choose a language that provides automatic memory management.
Implementation
Ensure that each allocation is freed only once. After freeing a chunk, set the pointer to NULL to ensure the pointer cannot be freed again. In complicated error conditions, be sure that clean-up routines respect the state of allocation properly.
Implementation
Use a static analysis tool to find double free instances.
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)
From MITRE CWE, MITRE CAPEC and OWASP (Top 10, OpenCRE).

References

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Exploitation evidence

What to do

Affected software

Description

AI analysisMachine-generated, updated 10 Jul 2025, 19:05 UTC

WeaknessesCWE-415

Technical details

References

Community reviews

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