What is the ruling on hanging posters, news, invitations to political parties and other such posters in a mosque?

All perfect praise be to Allaah, The Lord of the worlds. I testify that there is none worthy of worship except Allaah, and that Muhammad, sallallaahu ‘alayhi wa sallam, is His slave and Messenger.

There is no harm to do what is beneficial for Islam and the Muslims in a mosque. This is because the mosque is as Shaykh Al-Bassaam said in Sharh Buloogh Al-Maraam: “In the earliest era (of Islam), it (i.e. mosque) was a place for teaching and preparing armies and in which the caliph would give glad tidings of Islamic conquests. Also, Hassaan (ibn Thaabit) used to recite poetry in it during the life of the Prophet, sallallaahu ‘alayhi wa sallam, as it was reported in Saheeh Al-Bukhari from Sa‘eed ibn Al-Musayyab that ‘Umar came to the mosque while Hassaan was reciting a poem (and he disapproved of it). Upon that, Hassaan said: 'I used to recite poetry in this very mosque in the presence of one (i.e. the Prophet) who was better than you.'”

Accordingly, there is no harm in posting news that is important to Muslims and giving them glad tidings or pointing out to them the tragedies of their devastated fellow Muslims all over the world. As for images, it is prohibited to hang or attach them to the wall of a mosque as there is no necessity for this. This is because images prevent angels from entering and it is one of the traditions of the Christians. 

In this effect, Abu Talhah narrated that the Messenger of Allaah, sallallaahu ‘alayhi wa sallam, said: “The angels do not enter a house in which there is a dog or an image.” [Al-Bukhari and Muslim]

Also, it was reported from ‘Aa’ishah that Umm Habeebah and Umm Salamah made mention of a church they saw in Ethiopia in which there were images. They told the Prophet, sallallaahu ‘alayhi wa sallam, about it and he said: “These are people whom, if a righteous man among them died, would build a place of worship over his grave and (hang) images in it. These are the most evil of creation before Allaah.” [Al-Bukhari and Muslim]