CVE-2026-21895VulnerabilityPublished 8 Jan 2026

CVE-2026-21895: RustCrypto RSA · Improper Check or Handling of Exceptional Conditions

Affects RustCrypto RSASource CVE Database V5

Not known to be exploited · CVSS 2.7 Low : upgrade to 0.9.10 when convenient.

Data as of 26 Oct 2026, 06:26 UTC

CVSS 4.0 base score

2.7Low

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

EPSS: 0.4% chance of exploitation in 30 days – higher than 38% of CVEsExploit Prediction Scoring System: the likelihood attackers will use this flaw soon.
Patch: Available – fixed in 0.9.10

CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:N/VI:N/VA:L/SC:N/SI:N/SA:N/E:U

Base metrics

Attack Vector: Network
Attack Complexity: Low
Attack Requirements: None
Privileges Required: None
User Interaction: None
Vulnerable system confidentiality: None
Vulnerable system integrity: None
Vulnerable system availability: Low
Subsequent system confidentiality: None
Subsequent system integrity: None
Subsequent system availability: None

Threat metrics

Exploit Maturity: Unreported

Bold values are the worst case: easiest to exploit or largest impact.

Attack Vector: Network: The vulnerable system is bound to the network stack and the set of possible attackers extends beyond the other options listed below, 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: The attacker must take no measurable action to exploit the vulnerability. The attack requires no target-specific circumvention to exploit the vulnerability. An attacker can expect repeatable success against the vulnerable system.
Attack Requirements: None: The successful attack does not depend on the deployment and execution conditions of the vulnerable system. The attacker can expect to be able to reach the vulnerability and execute the exploit under all or most instances of the vulnerability.
Privileges Required: None: The attacker is unauthorized prior to attack, and therefore does not require any access to settings or files of the vulnerable system to carry out an attack.
User Interaction: None: The vulnerable system can be exploited without interaction from any human user, other than the attacker.
Vulnerable system confidentiality: None: There is no loss of confidentiality within the Vulnerable System.
Vulnerable system integrity: None: There is no loss of integrity within the Vulnerable System.
Vulnerable system availability: Low: Performance is reduced or there are interruptions in resource availability. Even if repeated exploitation of the vulnerability is possible, the attacker does not have the ability to completely deny service to legitimate users. The resources in the Vulnerable System are either partially available all of the time, or fully available only some of the time, but overall there is no direct, serious consequence to the Vulnerable System.
Subsequent system confidentiality: None: There is no loss of confidentiality within the Subsequent System or all confidentiality impact is constrained to the Vulnerable System.
Subsequent system integrity: None: There is no loss of integrity within the Subsequent System or all integrity impact is constrained to the Vulnerable System.
Subsequent system availability: None: There is no impact to availability within the Subsequent System or all availability impact is constrained to the Vulnerable System.
Exploit Maturity: Unreported: Based on threat intelligence sources each of the following must apply: · No knowledge of publicly available proof-of-concept · No knowledge of reported attempts to exploit this vulnerability · No knowledge of publicly available solutions used to simplify attempts to exploit the vulnerability

Definitions: FIRST CVSS v4.0 specification.

Exploitation evidence

Disclosed: evidence found.
CVE published 8 Jan 2026
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 RSA and rustcrypto/rsa to 0.9.10.

Affected software

Product	Affected	Fixed in
RustCryptoRSA	Affected <0.9.10	Fixed in 0.9.10
crates.iorustcrypto/rsa`pkg:cargo/rustcrypto/rsa`Other threats	Affected <0.9.10	Fixed in 0.9.10

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-2026-21895, European organizations should: 1) Upgrade all RustCrypto RSA crate dependencies to version 0.9.10 or later, where the issue is fixed. 2) Audit code that constructs RSA private keys from components to ensure proper validation of prime factors and error handling, preventing panics from propagating. 3) Implement input validation and sanitization for any externally sourced RSA key components to reject invalid primes such as 1 before key construction. 4) Incorporate robust exception handling around cryptographic operations to gracefully handle unexpected errors without crashing the application. 5) Monitor application logs for panic events related to RSA key handling to detect potential exploitation attempts or malformed inputs. 6) For critical systems, consider adding redundancy or failover mechanisms to minimize service disruption from potential DoS caused by this vulnerability. 7) Engage with RustCrypto community updates and security advisories to stay informed about related vulnerabilities and patches.

Description

The `rsa` crate is an RSA implementation written in rust. Prior to version 0.9.10, when creating a RSA private key from its components, the construction panics instead of returning an error when one of the primes is `1`. Version 0.9.10 fixes the issue.

Impact

For European organizations, the primary impact of CVE-2026-21895 is the potential for denial-of-service conditions in applications that use vulnerable versions of the RustCrypto RSA crate. This could disrupt services that rely on RSA key operations, such as secure communications, authentication, or digital signatures. While the vulnerability does not compromise confidentiality or integrity of cryptographic keys, unexpected application crashes can affect availability and reliability of critical systems. Organizations in sectors with high reliance on Rust-based cryptographic libraries—such as financial services, telecommunications, and government agencies—may experience operational disruptions if they process malformed RSA key components. The impact is more pronounced in environments where RSA keys are dynamically generated or imported from untrusted sources without sufficient validation. Given the low CVSS score and absence of known exploits, the threat is moderate but should not be ignored, especially in high-availability or security-sensitive contexts.

CWE-703Improper Check or Handling of Exceptional Conditions (opens in a new tab)
Pillar weaknessOWASP Top 10 A10:2025: Mishandling of Exceptional Conditions (opens in a new tab)
The product does not properly anticipate or handle exceptional conditions that rarely occur during normal operation of the product.
MITRE discourages mapping vulnerabilities to this broad entry; the root cause is usually a more specific weakness.
OWASP Cheat Sheets
Logging (opens in a new tab)
Error Handling (opens in a new tab)
From MITRE CWE, MITRE CAPEC and OWASP (Top 10, OpenCRE).

References

Community reviews

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Exploitation evidence

What to do

Affected software

Description

AI analysisMachine-generated, updated 8 Jan 2026, 14:34 UTC

WeaknessesCWE-703

Technical details

References

Community reviews

Related threats