Caley Thistle led through Gregory Tade's diving header until the 86th-minute equaliser at Tulloch Caledonian Stadium.
Tade's close-range header put the Highlanders ahead after 33 minutes but David Proctor's trip on Buchanan gave the Pars the chance to level things and prevent bottom side Inverness from replacing them in ninth.
Caley Thistle remain a point adrift, with Dunfermline immediately above them.
The Pars had taken only one point in their last six matches prior to the game, while Inverness are now four games unbeaten at home.
Caley Thistle manager Terry Butcher named an unchanged line-up for the third successive game despite going down 2-0 at St Johnstone last week.
Visiting manager Jim McIntyre made two changes to the side who lost 2-0 at home to Hearts last week with on-loan Jason Thomson and Alex Keddie coming in for Ryan Thomson and Andy Dowie.
Chances were at a premium in the opening stages with Caley Thistle's Andrew Shinnie managing to evade his marker to reach the by-line for the hosts in the highlight of the first quarter hour but his cross failed to find Nick Ross.
Returning on-loan Hearts player Jason Thomson provided much of the attacking intent for the visitors, picking out Andy Kirk in a prime position but he was offside.
David Graham blew his chance when he was found in space by Paul Burns as he ballooned his chance over from the edge of the area.
Burns almost snatched a surprise lead after 21 minutes when a Joe Cardle corner was only marginally cleared as far as the midfielder who sent in a curling effort which caught keeper Ryan Esson flat-footed, with only the woodwork denying an opening goal.
Dunfermline's Keddie was on hand to stop Ross breaking the deadlock.
The defender blocked the midfielder's shot following good work from Tade.
On the counter John Potter's header was saved at point-blank range by home keeper Esson following another Cardle corner.
Esson was again the hero moments later when he saved Cardle's 16-yard thunderbolt.
At the opposite end Tade was the star man with a terrific header to put Inverness in front after 33 minutes.
The Frenchman's close-range full-stretch diving header was his fourth goal of the season after being set up by strike-partner Richie Foran's cross.
Greg Tansey could have notched a second when he connected to Shinnie's cross but the header was kept out by Pars keeper Paul Gallagher.
Graham tested Esson with a 25-yard shot as Dunfermline hunted an equaliser after the interval, but the stopper was equal to it.
Tade's cross was just wide moments later when he might have doubled the lead.
Esson helped preserve the narrow lead just after the hour when he saved Buchanan's piledriver after he connected with fellow sub Ryan Thomson's cut-back.
Inverness introduced Josh Meekings and Lee Cox for their first appearances of the season but both failed to make a telling impact.
Foran found Ross but his angled effort was saved well by Gallagher before Buchanan equalised with four minutes to go.
Referee Steven McLean awarded a penalty after Buchanan was tripped by Inverness centre back Proctor.
Buchanan sent Esson the wrong way as he drilled the spot kick low into the net.
Gary Mason might have hit a last-gasp winner for the visitors but he fired inches wide as he met a cross from substitute Steven McDougall.
There was still time for Inverness substitute Shane Sutherland to try his luck at the death but Gallagher's diving save ensured both sides would have to share the spoils.