CVE-2020-26263: Tlslite ng RSA Weakness Vulnerability

Q: What is CVE-2020-26263?

CVE-2020-26263 is a security vulnerability in Tlslite ng involving RSA weakness in tslite-ng under CWE-326: Inadequate Encryption Strength.

Q: Which Tlslite ng versions are affected?

Affected versions include releases prior to 0.7.6 across affected packages: tlslite-ng.

Q: What version fixes CVE-2020-26263?

Upgrading to 0.7.6 (or the latest patched release for your respective branch) resolves the vulnerability.

Q: Is tlslite-ng affected?

Yes, tlslite-ng is affected in releases prior to 0.7.6. Upgrade your dependency to 0.7.6 or later.

Q: What is the CVSS score of CVE-2020-26263?

CVE-2020-26263 has a CVSS v3.1 base score of 7.5 (HIGH) with vector string CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:H/A:N.

Q: What CWE is associated with CVE-2020-26263?

CVE-2020-26263 is classified under CWE-326: Inadequate Encryption Strength (The product stores or transmits sensitive data using an encryption scheme that is theoretically sound, but is not strong enough for the level of protection required.).

Q: How can I check PyPI dependencies for CVE-2020-26263?

Run the dependency tree command: 'pip show tlslite-ng'. This command lists direct and transitive dependencies in your build configuration so you can verify if a vulnerable version is resolved.

HIGH

Advisory Identifier: GHSA-wvcv-832q-fjg7

CVSS 7.5

CWE-326

Published 2020-12-21

Advisory Summary

CVE-2020-26263 is a HIGH (CVSS 7.5) rsa weakness vulnerability (CWE-326: Inadequate Encryption Strength) affecting Tlslite ng libraries in the PyPI ecosystem. The issue involves rsa weakness in tslite-ng. Remediation is available by upgrading affected packages to version 0.7.6.

CVE-2020-26263 at a Glance

CVE Identifier CVE-2020-26263

GHSA Identifier GHSA-wvcv-832q-fjg7

Severity HIGH

CVSS v3.1 Base Score 7.5

CWE Classification CWE-326: Inadequate Encryption Strength

Affected Product Tlslite ng

Package Ecosystem PyPI

Published Date 2020-12-21

Last Updated 2024-11-13

Security Impact

CVSS: 7.5

The security impact metrics below are parsed directly from the CVSS v3.1 vector string (CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:H/A:N).

Attack Vector Network (AV:N)

Attack Complexity Low (AC:L)

Privileges Required None (PR:N)

User Interaction None (UI:N)

Scope Unchanged (S:U)

Confidentiality None (C:N)

Integrity High (I:H)

Availability None (A:N)

How to Fix CVE-2020-26263

To remediate this vulnerability, upgrade all affected Tlslite ng dependencies to a patched release. Both direct and transitive dependencies should be checked, as frameworks or security libraries may pull in vulnerable versions transitively.

tlslite-ng fixed: 0.7.6

pip install tlslite-ng>=0.7.6

Verify Direct and Transitive Dependencies

Run the following command in your project directory to verify that all resolved dependencies use the patched release:

pip show tlslite-ng

How to Check if You Are Affected

To determine whether your Python environment is affected by CVE-2020-26263, inspect your installed packages using pip:

pip show tlslite-ng

Analyze the terminal output to locate any version of Tlslite ng in your dependency tree. If any resolved version matches the vulnerable ranges listed in the table below (for example, versions earlier than 0.7.6), your application is affected.

Note: The pip show tlslite-ng command checks currently installed packages in your active Python environment.

Technical Details

Vulnerability Mechanism & Technical Analysis

This vulnerability is classified under CWE-326: Inadequate Encryption Strength, where the product stores or transmits sensitive data using an encryption scheme that is theoretically sound, but is not strong enough for the level of protection required. In Tlslite ng, software state validation or input boundaries are circumvented during processing. Review the official source advisory statement below for specific affected components, classes, and reproduction details.

Source Advisory Statement

### Impact The code that performs decryption and padding check in RSA PKCS#1 v1.5 decryption is data dependant. In particular, code in current (as of 0.8.0-alpha38) master https://github.com/tlsfuzzer/tlslite-ng/blob/0812ed60860fa61a6573b2c0e18771414958f46d/tlslite/utils/rsakey.py#L407-L441 and code in 0.7.5 branch https://github.com/tlsfuzzer/tlslite-ng/blob/acdde3161124d6ae37c506b3476aea9996d12e97/tlslite/utils/rsakey.py#L394-L425 has multiple ways in which it leaks information (for one, it aborts as soon as the plaintext doesn't start with 0x00, 0x02) about the decrypted ciphertext (both the bit length of the decrypted message as well as where the first unexpected byte lays). All TLS servers that enable RSA key exchange as well as applications that use the RSA decryption API directly are vulnerable. All previous versions of tlslite-ng are vulnerable. ### Patches The patches to fix it are proposed in https://github.com/tlsfuzzer/tlslite-ng/pull/438 https://github.com/tlsfuzzer/tlslite-ng/pull/439 Note: the patches depend on Python processing the individual bytes in side-channel free manner, this is known to not be the case: https://securitypitfalls.wordpress.com/2018/08/03/constant-time-compare-in-python/ As such, users that require side-channel resistance are recommended to use different TLS implementations, as stated in the [security policy](https://github.com/tlsfuzzer/tlslite-ng/blob/master/SECURITY.md) of tlslite-ng. ### Workarounds There is no way to workaround this issue. ### References https://securitypitfalls.wordpress.com/2018/08/03/constant-time-compare-in-python/ ### For more information If you have any questions or comments about this advisory please open an issue in [tlslite-ng](https://github.com/tlsfuzzer/tlslite-ng/issues).

CVE-2020-26263 Affected Tlslite ng Versions

1 component(s)

Fixed Versions:

0.7.6

Product / Package	Ecosystem	Affected Versions	Fixed Version
tlslite-ng pypi/tlslite-ng	PyPI	< 0.7.6	0.7.6

References

GitHub Advisory / Wiki ADVISORY

https://github.com/tlsfuzzer/tlslite-ng/security/advisories/GHSA-wvcv-832q-fjg7

NVD — CVE-2020-26263 NVD

https://nvd.nist.gov/vuln/detail/CVE-2020-26263

Tlslite ng Source Repository REPOSITORY

https://github.com/tlsfuzzer/tlslite-ng/pull/438

Tlslite ng Source Repository REPOSITORY

https://github.com/tlsfuzzer/tlslite-ng/pull/439

Security Fix Commit FIX COMMIT

https://github.com/tlsfuzzer/tlslite-ng/commit/c28d6d387bba59d8bd5cb3ba15edc42edf54b368

Tlslite ng Source Repository REPOSITORY

https://github.com/pypa/advisory-database/tree/main/vulns/tlslite-ng/PYSEC-2020-143.yaml

Tlslite ng Source Repository REPOSITORY

https://github.com/tlsfuzzer/tlslite-ng

pypi.org/project/tlslite-ng WEB

https://pypi.org/project/tlslite-ng

Tlslite ng Security Information SECURITY

https://securitypitfalls.wordpress.com/2018/08/03/constant-time-compare-in-python

Frequently Asked Questions

What is CVE-2020-26263?

CVE-2020-26263 is a security vulnerability in Tlslite ng involving RSA weakness in tslite-ng under CWE-326: Inadequate Encryption Strength.

Which Tlslite ng versions are affected?

Affected versions include releases prior to 0.7.6 across affected packages: tlslite-ng.

What version fixes CVE-2020-26263?

Upgrading to 0.7.6 (or the latest patched release for your respective branch) resolves the vulnerability.

Is tlslite-ng affected?

Yes, tlslite-ng is affected in releases prior to 0.7.6. Upgrade your dependency to 0.7.6 or later.

What is the CVSS score of CVE-2020-26263?

CVE-2020-26263 has a CVSS v3.1 base score of 7.5 (HIGH) with vector string CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:H/A:N.

What CWE is associated with CVE-2020-26263?

CVE-2020-26263 is classified under CWE-326: Inadequate Encryption Strength (The product stores or transmits sensitive data using an encryption scheme that is theoretically sound, but is not strong enough for the level of protection required.).

How can I check PyPI dependencies for CVE-2020-26263?

Run the dependency tree command: 'pip show tlslite-ng'. This command lists direct and transitive dependencies in your build configuration so you can verify if a vulnerable version is resolved.

Machine-readable OSV JSON OSV v1.5 Schema

Normalized schema output

View Raw JSON

{
  "schema_version" : "1.4.0",
  "id" : "GHSA-wvcv-832q-fjg7",
  "modified" : "2024-11-13T23:01:33Z",
  "published" : "2020-12-21T16:56:37Z",
  "aliases" : [ "CVE-2020-26263" ],
  "summary" : "RSA weakness in tslite-ng",
  "details" : "### Impact\nThe code that performs decryption and padding check in RSA PKCS#1 v1.5 decryption is data dependant.\nIn particular, code in current (as of 0.8.0-alpha38) master\nhttps://github.com/tlsfuzzer/tlslite-ng/blob/0812ed60860fa61a6573b2c0e18771414958f46d/tlslite/utils/rsakey.py#L407-L441\nand code in 0.7.5 branch\nhttps://github.com/tlsfuzzer/tlslite-ng/blob/acdde3161124d6ae37c506b3476aea9996d12e97/tlslite/utils/rsakey.py#L394-L425\nhas multiple ways in which it leaks information (for one, it aborts as soon as the plaintext doesn't start with 0x00, 0x02) about the decrypted ciphertext (both the bit length of the decrypted message as well as where the first unexpected byte lays).\n\nAll TLS servers that enable RSA key exchange as well as applications that use the RSA decryption API directly are vulnerable.\n\nAll previous versions of tlslite-ng are vulnerable.\n\n### Patches\nThe patches to fix it are proposed in \nhttps://github.com/tlsfuzzer/tlslite-ng/pull/438\nhttps://github.com/tlsfuzzer/tlslite-ng/pull/439\n\nNote: the patches depend on Python processing the individual bytes in side-channel free manner, this is known to not be the case: https://securitypitfalls.wordpress.com/2018/08/03/constant-time-compare-in-python/\nAs such, users that require side-channel resistance are recommended to use different TLS implementations, as stated in the [security policy](https://github.com/tlsfuzzer/tlslite-ng/blob/master/SECURITY.md) of tlslite-ng.\n\n### Workarounds\nThere is no way to workaround this issue.\n\n### References\nhttps://securitypitfalls.wordpress.com/2018/08/03/constant-time-compare-in-python/\n\n### For more information\nIf you have any questions or comments about this advisory please open an issue in [tlslite-ng](https://github.com/tlsfuzzer/tlslite-ng/issues).",
  "severity" : [ {
    "type" : "CVSS_V3",
    "score" : "CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:H/A:N"
  }, {
    "type" : "CVSS_V4",
    "score" : "CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:N/VI:H/VA:N/SC:N/SI:N/SA:N"
  } ],
  "affected" : [ {
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      "name" : "tlslite-ng"
    },
    "ranges" : [ {
      "type" : "ECOSYSTEM",
      "events" : [ {
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      } ]
    } ]
  } ],
  "references" : [ {
    "type" : "WEB",
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  }, {
    "type" : "ADVISORY",
    "url" : "https://nvd.nist.gov/vuln/detail/CVE-2020-26263"
  }, {
    "type" : "WEB",
    "url" : "https://github.com/tlsfuzzer/tlslite-ng/pull/438"
  }, {
    "type" : "WEB",
    "url" : "https://github.com/tlsfuzzer/tlslite-ng/pull/439"
  }, {
    "type" : "WEB",
    "url" : "https://github.com/tlsfuzzer/tlslite-ng/commit/c28d6d387bba59d8bd5cb3ba15edc42edf54b368"
  }, {
    "type" : "WEB",
    "url" : "https://github.com/pypa/advisory-database/tree/main/vulns/tlslite-ng/PYSEC-2020-143.yaml"
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  }, {
    "type" : "WEB",
    "url" : "https://securitypitfalls.wordpress.com/2018/08/03/constant-time-compare-in-python"
  } ],
  "database_specific" : {
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    "severity" : "HIGH",
    "github_reviewed" : true,
    "github_reviewed_at" : "2020-12-21T16:55:47Z",
    "nvd_published_at" : null
  }
}

CVSS V3

7.5 HIGH

Attack Vector Network (AV:N)

Attack Complexity Low (AC:L)

Privileges Required None (PR:N)

User Interaction None (UI:N)

Scope Unchanged (S:U)

Confidentiality None (C:N)

Integrity High (I:H)

Availability None (A:N)

Vector String

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

Advisory Metadata

Source ID: GHSA-wvcv-832q-fjg7
Schema Version: 1.4.0
Published: 2020-12-21 16:56
Last Modified: 2024-11-13 23:01
Database Record File: advisories/github-reviewed/2020/12/GHSA-wvcv-832q-fjg7/GHSA-wvcv-832q-fjg7.json