CVE-2020-9818
Apple iOS, iPadOS, and watchOS Out-of-Bounds Write Vulnerability
Description
CVE-2020-9818 is a high-severity out-of-bounds write vulnerability in Apple iOS, iPadOS, and watchOS Mail. The flaw allows an attacker to trigger unexpected memory modification or application termination by sending a maliciously crafted mail message. CISA has added this vulnerability to its Known Exploited Vulnerabilities (KEV) catalog, confirming active exploitation in the wild. With an EPSS score of 0.25% (48.4th percentile), CVE-2020-9818 represents a serious remote threat to Apple mobile devices through the Mail application.
KEV Information
CVSS Score
CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:H/I:H/A:HOpen in CalculatorAffected Products
| Vendor | Product | Version |
|---|---|---|
| apple | ipados | < 13.5 |
| apple | iphone os | < 12.4.7; >= 13.0, < 13.5 |
| apple | watchos | < 6.2.5 |
Multiple CVSS Assessments
CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:H/I:H/A:H
CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:H/I:H/A:H
References
- https://support.apple.com/HT211168(Release Notes, Vendor Advisory)
- https://support.apple.com/HT211169(Release Notes, Vendor Advisory)
- https://support.apple.com/HT211175(Release Notes, Vendor Advisory)
- https://www.cisa.gov/known-exploited-vulnerabilities-catalog?field_cve=CVE-2020-9818(US Government Resource)
Weakness Type
CWE-787: Out-of-bounds Write
Out-of-bounds write vulnerabilities occur when software writes data beyond the intended boundaries of a memory buffer. In CVE-2020-9818, insufficient bounds checking in the Apple Mail application allows a specially crafted email message to write outside allocated memory regions, potentially corrupting adjacent data structures and enabling memory modification or application crashes.
Learn more: CWE-787 — Out-of-bounds Write
Impact Analysis
CVE-2020-9818 carries a CVSS 3.1 score of 8.8 (HIGH), indicating a severe threat. The vulnerability is remotely exploitable over the network with low attack complexity and requires no authentication, though user interaction is needed in the form of processing a malicious email. Successful exploitation results in high impact to confidentiality, integrity, and availability, as the out-of-bounds write can lead to memory modification that may enable further code execution or cause application termination. Organizations relying on Apple Mail on iOS, iPadOS, or watchOS devices face significant risk from this vulnerability, as email-based attack vectors are particularly effective for targeted attacks.
Exploit Maturity
CVE-2020-9818 is confirmed as actively exploited through its inclusion in the CISA Known Exploited Vulnerabilities catalog. The EPSS score of 0.25% (48.4th percentile) suggests moderate but real exploitation probability. No public exploit code was identified in the available references, but the active exploitation status confirmed by CISA indicates that threat actors have developed working exploits. Federal agencies were required to remediate this vulnerability by 2022-05-03 per CISA's binding operational directive.
Remediation
- Apply vendor patches immediately as mandated by CISA KEV: Apply updates per vendor instructions. Update to iOS 13.5/iPadOS 13.5, iOS 12.4.7, or watchOS 6.2.5.
- For devices running older iOS versions, ensure at minimum iOS 12.4.7 is installed. For iPadOS, update to at least iPadOS 13.5. For Apple Watch, update watchOS to 6.2.5 or later.
- As an interim mitigation, consider disabling automatic mail fetching and configuring mail accounts to require manual refresh, reducing the window for automated exploitation of malicious messages.
- Monitor mail application behavior for unexpected crashes or termination, which may indicate exploitation attempts targeting this out-of-bounds write vulnerability.
- Implement email security controls such as mail filtering and attachment scanning at the gateway level to detect and block maliciously crafted messages before they reach vulnerable devices.
Technical Details
CVE-2020-9818 is an out-of-bounds write vulnerability in the Apple Mail application across iOS, iPadOS, and watchOS. The flaw stems from insufficient bounds checking when processing email message content. According to the CVSS vector (CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:H/I:H/A:H), the vulnerability is network-accessible with low complexity and requires no privileges, though user interaction is needed. When the Mail application processes a maliciously crafted message, the parser fails to properly validate write boundaries, allowing data to be written beyond the allocated buffer. This can corrupt adjacent memory, leading to unexpected memory modification or application termination. Apple addressed this issue with improved bounds checking.
Frequently Asked Questions
Is CVE-2020-9818 being actively exploited?
Yes. CVE-2020-9818 is listed in the CISA Known Exploited Vulnerabilities catalog, confirming active exploitation. The EPSS score of 0.25% (48.4th percentile) indicates a moderate exploitation probability.
What products are affected by CVE-2020-9818?
CVE-2020-9818 affects Apple iPadOS (< 13.5), iPhone OS (< 12.4.7; >= 13.0, < 13.5), and watchOS (< 6.2.5). The vulnerability specifically targets the Mail application on these platforms.
How do I fix CVE-2020-9818?
Apply updates per vendor instructions. Update affected devices to iOS 13.5, iPadOS 13.5, iOS 12.4.7, or watchOS 6.2.5. If immediate patching is not possible, disable automatic mail fetching and implement email filtering at the gateway level.
How severe is CVE-2020-9818?
CVE-2020-9818 has a CVSS 3.1 score of 8.8 (HIGH). It is a remotely exploitable out-of-bounds write vulnerability in Apple Mail that can lead to memory corruption and application crashes, with confirmed active exploitation.
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