CVE-2021-43527
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Description
A remote code execution flaw was found in the way NSS verifies certificates. This flaw allows an attacker posing as an SSL/TLS server to trigger this issue in a client application compiled with NSS when it tries to initiate an SSL/TLS connection. Similarly, a server application compiled with NSS, which processes client certificates, can receive a malicious certificate via a client, triggering the flaw. The highest threat to this vulnerability is confidentiality, integrity, as well as system availability.
Security Bulletin
https://access.redhat.com/security/vulnerabilities/RHSB-2021-008
Statement
The issue is not limited to TLS. Any applications that use NSS certificate verification are vulnerable; S/MIME is impacted as well. Similarly, a server application compiled with NSS, which processes client certificates, can receive a malicious certificate via a client.
Firefox is not vulnerable to this flaw as it uses the mozilla::pkix for certificate verification. Thunderbird is affected when parsing email with the S/MIME signature. Thunderbird on Red Hat Enterprise Linux 8.4 and later does not need to be updated since it uses the system NSS library, but earlier Red Hat Enterprise Linux 8 extended life streams will need to update Thunderbird as well as NSS.
Mitigation
Red Hat has investigated whether a possible mitigation exists for this issue, and has not been able to identify a practical example. Please update the affected package as soon as possible.
Additional information
- Bugzilla 2024370: nss: Memory corruption in decodeECorDsaSignature with DSA signatures (and RSA-PSS)
- CWE-120: Buffer Copy without Checking Size of Input ('Classic Buffer Overflow')
- FAQ: Frequently asked questions about CVE-2021-43527
Common Vulnerability Scoring System (CVSS) Score Details
Important note
CVSS scores for open source components depend on vendor-specific factors (e.g. version or build chain). Therefore, Red Hat's score and impact rating can be different from NVD and other vendors. Red Hat remains the authoritative CVE Naming Authority (CNA) source for its products and services (see Red Hat classifications).
| Red Hat | NVD | |
|---|---|---|
CVSS v3 Base Score | 9.8 | 9.8 |
Attack Vector | Network | Network |
Attack Complexity | Low | Low |
Privileges Required | None | None |
User Interaction | None | None |
Scope | Unchanged | Unchanged |
Confidentiality Impact | High | High |
Integrity Impact | High | High |
Availability Impact | High | High |
CVSS v3 Vector
Red Hat: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H
NVD: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H
Understanding the Weakness (CWE)
Integrity,Confidentiality,Availability
Technical Impact: Modify Memory; Execute Unauthorized Code or Commands
Buffer overflows often can be used to execute arbitrary code, which is usually outside the scope of the product's implicit security policy. This can often be used to subvert any other security service.
Availability
Technical Impact: Modify Memory; DoS: Crash, Exit, or Restart; DoS: Resource Consumption (CPU)
Buffer overflows generally lead to crashes. Other attacks leading to lack of availability are possible, including putting the product into an infinite loop.
Acknowledgements
Red Hat would like to thank Tavis Ormandy (Project Zero) for reporting this issue. Upstream acknowledges the Mozilla project as the original reporter.
Frequently Asked Questions
Why is Red Hat's CVSS v3 score or Impact different from other vendors?
My product is listed as "Under investigation" or "Affected", when will Red Hat release a fix for this vulnerability?
What can I do if my product is listed as "Will not fix"?
What can I do if my product is listed as "Fix deferred"?
What is a mitigation?
I have a Red Hat product but it is not in the above list, is it affected?
Why is my security scanner reporting my product as vulnerable to this vulnerability even though my product version is fixed or not affected?
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