1870579 - (CVE-2024-4772) Use of insecure rand() function to generate cnonce value in HTTP digest auth

Status: RESOLVED FIXED

(Core :: Networking: HTTP, defect, P2)

Description

[Hanno Boeck]

The code for HTTP Digest authentication uses the rand() function to generate a random nonce value (the "cnonce").

This code in nsHttpDigestAuth.cpp:

  nsAutoCString cnonce;
  static const char hexChar[] = "0123456789abcdef";
  for (int i = 0; i < 16; ++i) {
    cnonce.Append(hexChar[(int)(15.0 * rand() / (RAND_MAX + 1.0))]);
  }

Here: https://searchfox.org/mozilla-central/source/netwerk/protocol/http/nsHttpDigestAuth.cpp#326

This should probably use some secure random function. (Like RNG_GenerateGlobalRandomBytes from NSS.)

I am marking this as a security bug, but I should say that I am unsure what the exact security impact is. I am not familiar with the inner workings of the HTTP Digest authentication protocol and what a predictable cnonce would cause. However, this can probably be used to leak information about the state of the rand() RNG to an attacker. This could be bad if rand() is also used in other problematic places.

Comment 1

[Frederik Braun [:freddy]]

Permalink https://searchfox.org/mozilla-central/rev/91cc8848427fdbbeb324e6ca56a0d08d32d3c308/netwerk/protocol/http/nsHttpDigestAuth.cpp#326

Comment 2

[Frederik Braun [:freddy]]

Looks like the "binary data to hex characters" bit is also broken and should use a common utility function instead.

Comment 3

[Kershaw Chang [:kershaw]]

Attachment: Bug 1870579 - Use PK11_GenerateRandom to generate random number, r=#necko

Comment 4

[Pulsebot]

Pushed by [e-mail]:
https://hg.mozilla.org/integration/autoland/rev/4c58e1b47bd6
Use PK11_GenerateRandom to generate random number, r=necko-reviewers,valentin

Comment 5

[Sebastian Hengst [:aryx] (needinfo me if it's about an intermittent or backout)]

https://hg.mozilla.org/mozilla-central/rev/4c58e1b47bd6

Comment 6

[BugBot [:suhaib / :marco/ :calixte]]

The patch landed in nightly and beta is affected.
:kershaw, is this bug important enough to require an uplift?

• If yes, please nominate the patch for beta approval.
• If no, please set status-firefox125 to wontfix.

For more information, please visit BugBot documentation.

Comment 7

[Daniel Veditz [:dveditz]]

Unfortunately this does not meet the severity level for our bug bounty program

Comment 8

[Jesse Schwartzentruber (:truber)]

Attachment: advisory.txt