Primary sources: mitmproxy commit, eMudhra statement

The open-source interception proxy mitmproxy has added an opt-in command-line option, --emudhra, that signs the TLS certificates it generates with the private key of a compromised eMudhra intermediate certificate authority, according to a commit merged on Wednesday, Oct. 21¹. The changelog lists it under unreleased changes for the next version¹.

The keys of eight eMudhra intermediate CAs were generated with insufficient randomness, which let anyone forge trusted HTTPS certificates against clients that still trust those CAs, Google's Chrome and Android security teams said on Tuesday². Mozilla said an attacker who could intercept a connection could use such certificates to impersonate websites and potentially read or modify traffic³.

The new option is off by default, according to the code¹. When it is turned on, mitmproxy loads a bundled private key and certificate chain for the intermediate named EM OV TLS CA - G3C and its cross-signed root, emSign Root TLS CA - G3¹. A test added in the same commit checks that a client trusting only the emSign ECC Root CA - G3 accepts a certificate mitmproxy issues with the option enabled¹. The commit and changelog do not state what the option is intended for¹.

The same changelog lists a separate change that updates mitmproxy's certifi dependency to remove eMudhra CAs from its precompiled binaries¹.

Chrome blocked the affected intermediates with a CRLSet update on Saturday, Oct. 17, and plans to remove emSign ECC Root CA - G3 from the Chrome Root Store in a release expected Tuesday, Oct. 27, Google said². Google said no TLS certificates chaining to the six affected TLS intermediates had been logged to Certificate Transparency before the block, so CT-enforcing clients such as Chrome could not have been targeted with them².

Mozilla said it blocked the certificates in Firefox through OneCRL within three hours of receiving the report on Oct. 17, released Firefox 158.0.1 and updated ESR versions on Tuesday, and is removing the root that signed the intermediates from NSS 3.131.1³.

eMudhra said it revoked all eight intermediates on Monday, Oct. 19, that seven were never used in production and that the one in production had not issued a certificate⁴. "No certificates had been issued from any of them, our infrastructure was not compromised, and no data was breached," the company said⁴.

The sources give different dates for the first report. Google said the Chrome Root Program received it on Oct. 17 at 18:05 UTC², while eMudhra said it was made aware late on the evening of Oct. 18, India time⁴.

Google said website operators with certificates chaining to emSign ECC Root CA - G3 must get new certificates from another hierarchy, and that it is reviewing whether eMudhra's remaining CA certificates should stay in the Chrome Root Store². mitmproxy had not said when the option will ship in a release¹.

Sources

1. mitmproxy (GitHub commit)Add `--emudhra` option (#8500)Oct 21, 7:36 PM
2. Google Chrome and Android Security TeamsProtecting Chrome and Android Users from Compromised eMudhra Intermediate CA CertificatesOct 20, 3:49 PM
3. Mozilla Security BlogProtecting Firefox users following the compromise of eMudhra intermediate certificates
4. eMudhraeMudhra Statement on Recent Certificate Security Incident

Read the original at mitmproxy (GitHub commit) ↗