The CM Draconis system is a well-studied, double-lined spectroscopic binary that is totally eclipsing and exhibits strong magnetic activity. Nearly one million photometric measurements have been collected across multiple wavelengths over more than half a century. In addition to showing frequent flare activity and apsidal motion, CM Dra also hosts a distant white dwarf and has been proposed to harbor a Jupiter-sized circumbinary companion. At only 47 light-years from Earth, it remains one of the most observationally rich and dynamically intriguing low-mass binary systems. We present a comprehensive photometric and spectroscopic analysis of the system using new ground-based observations and data from 19 sectors of the TESS mission. We derive precise fundamental parameters for both components: M₁ = 0. 2307 0. 0008\, M_, M₂ = 0. 2136 0. 0008\, M_, R₁ = 0. 2638 0. 0011\, R_, R₂ = 0. 2458 0. 0010\, R_, L₁ = 0. 0060 0. 0005\, L_, and L₂ = 0. 0050 0. 0004\, L_. The derived distance (14. 4 0. 6 pc) is consistent with Gaia DR3 measurements. Eclipse timing variations (ETVs) spanning over five decades were analyzed in detail. A long-period (56 yr) modulation was identified, which may be attributed either to the light-time effect of a possible circumbinary companion or to magnetic activity cycles. While the Bayesian Information Criterion statistically favors the model involving a light-time effect from a planetary companion, stellar activity remains a viable alternative that cannot yet be ruled out. Our results demonstrate that CM Dra is a valuable test case for studying both stellar activity and the potential presence of circumbinary companions in multiple-star systems. Continued long-term monitoring will be essential to distinguish between these competing scenarios.
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