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CVE-2020-26149

Sensitive data exposure in NATS

7.5 HighFix available

NATS nats.js before 2.0.0-209, nats.ws before 1.0.0-111, and nats.deno before 1.0.0-9 allow credential disclosure from a client to a server.

Attack profile

How easy it is to exploit

Attack vector
Network
Complexity
Low
Privileges needed
None
User interaction
None

What an attacker can affect

Confidentiality
High
Integrity
None
Availability
None

Exploit likelihood

1.48%Up 0.6 points since Apr 14, 2021
90%50%10%1%

What each source reports

NVD Score used 7.5

NATS nats.js before 2.0.0-209, nats.ws before 1.0.0-111, and nats.deno before 1.0.0-9 allow credential disclosure from a client to a server.

Record
CVE-2020-26149
CVSS 3.1
7.5 HighCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:N/A:N
CVSS 2.0
5.0 MediumAV:N/AC:L/Au:N/C:P/I:N/A:N
Weakness
CWE-522
Updated
2026-11-02
CVE List No score

NATS nats.js before 2.0.0-209, nats.ws before 1.0.0-111, and nats.deno before 1.0.0-9 allow credential disclosure from a client to a server.

Record
CVE-2020-26149
Updated
2026-11-02
EUVDEUVD-2020-1419 No score

NATS nats.js before 2.0.0-209, nats.ws before 1.0.0-111, and nats.deno before 1.0.0-9 allow credential disclosure from a client to a server.

Record
EUVD-2020-1419
Updated
2026-11-03
GitHub AdvisoriesGHSA-82rf-q3pr-4f6p 7.5

Sensitive data exposure in NATS

Preview versions of two NPM packages and one Deno package from the NATS project contain an information disclosure flaw, leaking options to the NATS server; for one package, this includes TLS private credentials.

The _connection_ configuration options in these JavaScript-based implementations were fully serialized and sent to the server in the client's CONNECT message, immediately after TLS establishment.

The nats.js client supports Mutual TLS and the credentials for the TLS client key are included in the connection configuration options; disclosure of the client's TLS private key to the server has been observed.

Most authentication mechanisms are handled after connection, instead of as part of connection, so other authentication mechanisms are unaffected. For clarity: NATS account NKey authentication is NOT affected.

Neither the nats.ws nor the nats.deno clients support Mutual TLS: the affected versions listed below are those where the logic flaw is present. We are including the nats.ws and nats.deno versions out of an abundance of caution, as library maintainers, but rate as minimal the likelihood of applications leaking sensitive data.

Security impact:

  • NPM package nats.js:
  • mainline is unaffected
  • beta branch is vulnerable from 2.0.0-201, fixed in 2.0.0-209

Logic flaw:

  • NPM package nats.ws:
  • status: preview
  • flawed from 1.0.0-85, fixed in 1.0.0-111
  • status: preview
  • flawed in all git tags prior to fix
  • fixed with git tag v1.0.0-9

Impact:

For deployments using TLS client certificates (for mutual TLS), private key material for TLS is leaked from the client application to the server. If the server is untrusted (run by a third party), or if the client application also disables TLS verification (and so the true identity of the server is unverifiable) then authentication credentials are leaked.

Record
GHSA-82rf-q3pr-4f6p
CVSS 3.1
7.5 HighCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:N/A:N
Weakness
CWE-522
Updated
2026-11-02
OSV 7.5

NATS nats.js before 2.0.0-209, nats.ws before 1.0.0-111, and nats.deno before 1.0.0-9 allow credential disclosure from a client to a server.

Record
CVE-2020-26149
CVSS 3.1
7.5 HighCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:N/A:N
Updated
2026-11-02
OSVGHSA-82rf-q3pr-4f6p 7.5

Sensitive data exposure in NATS

Preview versions of two NPM packages and one Deno package from the NATS project contain an information disclosure flaw, leaking options to the NATS server; for one package, this includes TLS private credentials.

The _connection_ configuration options in these JavaScript-based implementations were fully serialized and sent to the server in the client's CONNECT message, immediately after TLS establishment.

The nats.js client supports Mutual TLS and the credentials for the TLS client key are included in the connection configuration options; disclosure of the client's TLS private key to the server has been observed.

Most authentication mechanisms are handled after connection, instead of as part of connection, so other authentication mechanisms are unaffected. For clarity: NATS account NKey authentication is NOT affected.

Neither the nats.ws nor the nats.deno clients support Mutual TLS: the affected versions listed below are those where the logic flaw is present. We are including the nats.ws and nats.deno versions out of an abundance of caution, as library maintainers, but rate as minimal the likelihood of applications leaking sensitive data.

Security impact:

  • NPM package nats.js:
  • mainline is unaffected
  • beta branch is vulnerable from 2.0.0-201, fixed in 2.0.0-209

Logic flaw:

  • NPM package nats.ws:
  • status: preview
  • flawed from 1.0.0-85, fixed in 1.0.0-111
  • status: preview
  • flawed in all git tags prior to fix
  • fixed with git tag v1.0.0-9

Impact:

For deployments using TLS client certificates (for mutual TLS), private key material for TLS is leaked from the client application to the server. If the server is untrusted (run by a third party), or if the client application also disables TLS verification (and so the true identity of the server is unverifiable) then authentication credentials are leaked.

Record
GHSA-82rf-q3pr-4f6p
CVSS 3.1
7.5 HighCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:N/A:N
Weakness
CWE-522
Updated
2026-11-02

Affected products

Affected packages

Affected packages
PackageAffectedFixed
nats
npm
2.0.0-201 to 2.0.0-206
2.0.0-209
nats.ws
npm
1.0.0-85 to 1.0.0-110
1.0.0-111
nats
npm
2.0.0-201 up to 2.0.0-209
2.0.0-209
nats.ws
npm
1.0.0-85 up to 1.0.0-111
1.0.0-111

History

History
RecordedChangedSources
aliasesEUVD
first indexedCVE List, GitHub Advisories, NVD, OSV

Dates are when Every CVE recorded each change. Upstream dates may differ.

In short

CVE-2020-26149 is a high vulnerability (CVSS 7.5) in Linuxfoundation Nats.deno, published September 30, 2020. No source lists public exploit code. EPSS puts the chance of exploitation in the next 30 days at 1.48%, the 74th percentile. Fixed in nats 2.0.0-209.

References

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