omainkeys identified mail) is an email. How the dkim l= tag works authentication australia telegram data protocol. That ensures that the content of your email has not been tampered with during transmission. It allows the recipient to verify that the email is indeed sent. And authorized by the domain owner.
When intermediary servers forward your email. They may change the email body. They may add extra information to the footer or the email body. The dkim l tag was introduced to prevent your legitimate email from failing. Dkim when the content is modified during forwarding or by mailing lists.
How the dkim l= tag works
Specify length : the l= tag is followed by an integer representing. The number of bytes of the message body that the dkim signature covers.
Partial body signature : by specifying a length ai for marketing leaders: the complete guide for cmos to succeed in 2025 only the first ‘n’ bytes of the body will be included in the hash used to generate the dkim signature. Any modifications to the body beyond this length will not affect dkim signature verification.
Example: dkim signature with l-tag dkim vulnerability
For example, a message body is 1000 bytes long, but only the first 500 bytes are signed:
However, a team of analysts at zone
Dkim-signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=notify. Domain. Com; s=selector1; t=1718098168; [email protected]; l=500; bh=sf9k/azh8do2xdyzlotjrmhj5txv4h4qjhfr+q3asum=; h=subject：message-id:to:date:content-type:from:from:to:cc:subject; b=h0jp5xjzsjuo06er2gm5k0fvt0cuc0xonfobu1oyaft2ugvxy0h/xly6x/e/ppt2s
In this example l=500 means that the. Dkim signature only includes the first 500 bytes of the email body.
However, a team of analysts at zone. Eu, a leading european domain registrar, has discovered a serious vulnerability related to the l-tag in dkim signatures. Aside from its benefits in email forwarding situations, cybercriminals can easily exploit the l-tag to send phishing emails that still pass dkim checks .
Dkim l= tag vulnerability
We do not recommend using the dkim l= tag because it weakens uk data your security posture and. Makes your domain vulnerable even if email authentication is configured.
An attacker can change the content of the message body and attach. A malicious file or link outside the byte range defined by the “L” tag in the unsigned portion of the message. When this email reaches your recipient, it will pass dkim. Subsequently, if dmarc is enabled for your domain , it will also pass.