CVE-2025-5262VulnerabilityPublished 27 May 2025Updated 25 Aug 2025

CVE-2025-5262: Mozilla Thunderbird · Double-free in libvpx encoder

Affects Mozilla ThunderbirdSource CVE Database V5

Not known to be exploited · CVSS 7.5 High : upgrade to 139 or 128.11 soon.

Data as of 26 Oct 2026, 07:57 UTC

CVSS 3.1 base score

7.5High

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

EPSS: 0.4% chance of exploitation in 30 days – higher than 39% of CVEsExploit Prediction Scoring System: the likelihood attackers will use this flaw soon.
Patch: Available – fixed in 139, 128.11

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 May 2025
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 2026-10-26.

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 Mozilla Thunderbird to 139 or 128.11.

Affected software

Product	Affected	Fixed in
Mozilla Thunderbird	Affected <139 <128.11	Fixed in 139 128.11

AI-suggested

To mitigate CVE-2025-5262, European organizations should prioritize updating Mozilla Thunderbird to versions 139 or later, or at least 128.11 or later, where the vulnerability has been addressed. In the absence of an immediate patch, organizations should consider disabling WebRTC functionality within Thunderbird to prevent triggering the vulnerable code path. Network-level controls such as filtering or blocking suspicious WebRTC traffic can reduce exposure. Employing application sandboxing or running Thunderbird with least privilege can limit the impact of potential exploitation. Monitoring Thunderbird process crashes and unusual behavior can provide early detection of exploitation attempts. Additionally, organizations should ensure that endpoint protection solutions are up to date and capable of detecting exploitation techniques related to memory corruption. Regular security awareness training for users to recognize phishing or malicious email attachments that could trigger WebRTC streams is also recommended. Finally, maintaining robust backup and incident response plans will help mitigate the impact if exploitation occurs.

Description

A double-free could have occurred in `vpx_codec_enc_init_multi` after a failed allocation when initializing the encoder for WebRTC. This could have caused memory corruption and a potentially exploitable crash. This vulnerability affects Thunderbird < 139 and Thunderbird < 128.11.

Impact

For European organizations, the impact of CVE-2025-5262 can be substantial, especially for those relying on Mozilla Thunderbird as a primary email client integrated with WebRTC functionalities for communication. Successful exploitation could lead to denial of service through application crashes, disrupting email and real-time communication workflows. More critically, if exploited for arbitrary code execution, attackers could gain control over affected systems, potentially leading to data breaches, lateral movement within networks, or deployment of malware. Given Thunderbird's use in both private and enterprise environments, this vulnerability could affect sensitive communications and data integrity. The lack of required privileges or user interaction lowers the barrier for attackers, increasing the risk of automated or targeted attacks. European organizations in sectors such as finance, government, healthcare, and critical infrastructure, which often use Thunderbird for secure communications, could face operational disruptions and increased exposure to cyber espionage or ransomware attacks if this vulnerability is exploited.

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 27 Aug 2025, 00:52 UTC

WeaknessesCWE-415

Technical details

References

Community reviews

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